Author's Note

Alright, I wanted to write this stuff down sooner rather then later, and I thought it would be good to explain how changelings in this AU differ from cannon.

Supplemental

The Seven Hives
The Seven Hives is the collective name given when refiring to the hives scattered throughout Equestria. The rulers of each hive are free to govern mostly as they please, however, in the case of a decision that would effect all of changeling kind, or in the event of a criminal trial where the ruler of the hive can not maintain and unbiased position, the rulers will gather together and cast a vote on what is to be done.

The hive mind
The hive mind is a magical connection that is shared between changelings of the same hive. It allows them to communicate as well as identify each other even while disguised, however this does not carry over to members of a different hive naturally.

Princess Cocoon and Princess Chrysalis were able to find a way to link themselves and the princesses of the other hives into a privet hive mind in which only the princesses can access, so far the closest any other changeling has come to this feat was when Queen Larva gained temporary access to the princesses privet hive mind.

Changeling magic and transformation
When a changeling disguises themselves, their body is physically changing, there are no illusions involved with the transformation.

Changelings naturally have the magic of all three tribes, albeit when spread out like this it does make them weaker when comparing them to an average member of a tribe e.g. a changeling usually has weaker unicorn magic then the average unicorn, thankfully changelings can shift the distribution of their magic into what ever type they need, even into the magic of other creatures but this is difficult to do.

When a changeling transforms, their body is reconstructed into the look that they desire, this means that they must have the organic materials necessary for the form they wish to take e.g. gemstones must be consumed for a changeling to replicate a crystal pony. It is possible for a changeling to partially transform, or transform into forms other than ponies, however it is noted to be more difficult to transform into forms the less 'pony like' they are, also the larger the change in size between the original form and the new transformation the greater the difficulty.

Types of changelings
There are five different classifications of changelings

1. Drones
2. Seekers
3. Guard
4. Goliath
5. Royal

Drones are the average changeling, they are the most abundant, their magic is not skewed in any one direction and can fill roles that can be meant for other changing types except for royals.

Seekers are the main scouts and love gatherers for hives, they often have stronger pegasus magic then unicorn or earth pony and are usually better at transformation, although this primarily is due to practice.

Guards are the main fighting force of the changeling hives, although due to the long years of peace not many have seen any real combat. Guards usually have much weaker then average pegasus magic but make up for it in improved unicorn and earth pony magic. Guards also mature faster, reaching adulthood at ten years old and have the shortest lifespans of the changing types, usually only reaching their fifties.

Goliaths are the largest type of regular changing, often reaching the hight of a fully grown alicorn, although some have become much larger then even that. Goliath magic is skewed towards earth pony magic, so they do much of the manual labour jobs of a hive. Goliaths are also the second longest lived and second slowest maturing type of changeling reaching adulthood at thirty and can age to be over two hundred years old.

Royals are the leaders of the hive, and are the strongest of all the changeling types, having near alicorn level magic in all three categories. Changeling royals are the only member of the species that can produce changeling offspring and are the slowest maturing and longest living of any changeling, reaching adulthood at eighty four and living for nearly three millennia. At the start of a royal changelings rule, they will lay a clutch of royal changeling eggs that will not hatch on their own, the parent must make the conscious decision to funnel love into the eggs to get them to hatch, this essentially ensures that a royal egg can not hatch in a time where the hive is low on love to feed the young royal.

Changeling biology
The natural look of a changeling will differ depending on the hive they originate from but they do share some commonalities. All changelings posses a sharp pointed horn and insectoid wings, the wings and the legs of changelings often have holes in them but this can vary from individual to individual, royal changeling horns are often crooked and bent. Changelings also sport a set of fangs which grow from their upper jaw and remain exposed to air when their mouth is closed. The body of a changeling are covered in a carapace that can come in a verity of colours, this carapace is often thicker on guards and goliaths, and thinner on seekers. All changeling types, with the exception of royals, have compound eyes that vary in colour depending on their hive. Royal changeling have much more mammalian eyes, much like those of a cat, contracting into slits. The colour of a changelings carapace and eyes are actually chosen by the first ruler of the hive, who undergo a complex ritual that changes their own natural carapace and eye colour, as well as the colour of their magical aura.

Different changeling types feature different ornamentation that can allow them to be differentiated at a glance. Royal ornamentation comes in the form of their hair which they often style and maintain much like a pony would. Guards have a series of short spines that run down their back, connected by a thin translucent membrane that is the same colour as their eyes. Seekers have grooves on the carapace of their legs, goliaths have the opposite, protrusions of extra carapace around their barrel. Drones have a fish like fin on the back of their necks.

Changelings are hermaphrodites, thus any changeling is capable of reproducing with any member of any sapient species. With royals, no matter their position in the exchange, they will receive a sample of their partners genetic marital and with that they can then use to begin producing eggs if they so choose. For non royal changelings, the offspring of the union will be the species of the non changeling parent, although it has been noted that pregnancies and egg laying involving changelings usually result in a higher then expected number of offspring. Two non royal changelings are incapable of reproducing.

Changeling culture
Due to their ability to transform, changelings can consume anything that any other species is capable of and more, however they do not gain the nutrition from these foods, so eating solid foods is seen as more of a activity done for pleasure then a need. As such most changeling dishes will usually be very flavourful and incorporate a verity of herbs and spices, many of which are poisonous to other species. This does come with the side effect of most disguised changelings often make very bland food for their non changeling friends and family, as it's easer to pass on the spices then memorise everything that non changelings can't eat. It is also worth noting that changeling are seemingly the only species to have made sweetened condensed milk, which features a lot in their cooking, this does lead to frustration for disguised changelings living far from the hives as they often can not make many of their favourite changeling foods.

Changelings are very communal creatures, often preferring to sleep in shared rooms then a room for just one changeling, this means that most changeling hives have one or more large communal bedrooms. Seekers and royals are generally exceptions to this as they spend large amounts of time outside of the hive and tend to pick up the habits and culture of those they spend time with. Changeling are also very open to visitors from other hives, as most changelings see the members of other hives much like ponies would see a distant relative.

Since changelings are hermaphrodites, they are not assigned a gender when they hatch, most tend to pick a gender to identify as when they choose a main disguise.

List of hives
Ponyville Hive (formally Coudsdale hive)
Ruled by Queen Meganeura (AKA Fairy Flight) the mother of Princess Anisoptera (AKA Rainbow dash).
The Ponyville is known for producing changelings that have an affinity towards pegasus and earth pony magic, as such many of their members when transformed into ponies tend to be above average fliers, or stronger then average earth ponies.
A member of The Ponyville Hive can be differentiated by their ultramarine blue carapace, red eyes, and red magical aura.

Canterlot Hive
Ruled by Queen Mantodea (AKA Star Searcher) the mother of Princess Hymenopus (AKA Lemon Hearts).
Much like members of the Ponyville hive with pegasus and earth pony magic, members of the Canterlot hive often display a higher then average affinity towards unicorn magic, a not insignificant amount of their members even attending Celestia's school for gifted unicorns.
A member of The Canterlot Hive can be differentiated by their yellow carapace, magenta eyes, and a magenta magical aura.

Manehattan Hive
Ruled by King Formicidae (AKA Gear Grinder) the father of Princess Acromyrmex (AKA Firecracker Burn).
The Manehattan hive is known for both their intelligence, as well as their stupidity, this stigma mainly comes from Princess Acromyrmex, who was inadvertently responsible for several large fires and extensive property damage throughout Manehattan history through her use of homemade explosives. Generally however, most members of the hive show great skill when working with machines and technology, and often export their skills to the other hives. It is also worth noting that The Manehatten Hive is the only hive in known changeling history where non changelings were raised alongside the changelings of the hive, these children were diamond dogs and were the result of an encounter their mother had with another diamond dog that she had spent some time with.
A member of The Manehatten Hive can be differentiated by a lime green carapace and black eyes, along with an ashy grey magical aura.

Las Pegasus Hive
Ruled by Queen Larva (AKA High Roller) who is the mother of Princess Chrysalis (AKA Crackle Cosette) and Princess Cocoon (AKA Broad Strokes).
The Las Pegasus Hive is the largest of the hives in terms of both territory and population, due to this their members often use their hive mind much more then members of the other hives, and have thus become experts in using it, having made dedicated channels that only certain discussion topics are to be communicated in, such as a channel dedicated to the collection of love, or to the running of the golden strings casino, which is the hives main source of income and is run directly by Queen larva.
A member of The Las Pegasus Hive can be differentiated by their ashy grey carapace, along with their teal eyes and emerald green magical aura.

The Frozen North Hive (formerly The Chrystal Empire Hive)
Ruled by Sovereign Diptera (AKA Clear Quartz) who is the parent of Princess Belgica (AKA Smoky Quartz)
Before The Crystal Empire disappeared, The Frozen North Hive would primarily feed off of the love given out by the crystal heart. However once the empire disappeared the hive had to find another source of love, which they found in their pets. Every single member of The Frozen North Hive keeps one or more pets, and through the many breeding programs for the animals in place it ensures that whenever a new changeling hatches they will have their own pet shortly after. This love is not as effective as getting it from other, more intelligent, species, so the seekers of the hive often make biyearly trips to Stalliongrad to gather more love and supplies for the hive, these supplies mainly being food and toys for their pets.
A member of The Frozen North Hive can be differentiated by their white carapace, eyes, and magical aura.

The Dragon Lands Hive.
Ruled by Queen Coleoptera (AKA Inferno) who is the mother of Princess Pheropsophus (AKA Ash).
As the name would implies, members of The Dragon Lands Hive spend most of their time around and disguised as dragons. Due to the differences between dragon and changeling physiology, the members of The Dragon Lands Hive are often much more competent at transforming then other changeling, and are often known to almost never fully return to their original form, and always keep some sort of transformation such as the organs necessary to breath fire. The Dragon Lands Hive is also known to have their members grow much larger then the average changeling, with the average drone being comparable to the tallest that a pony could grow to, this is even more pronounced in their goliaths who can grow to half the size of a full grown dragon.
A member of The Dragon Land Hive can be differentiated through their red carapace, and yellow eyes and magical aura.

The Griffonstone Hive
Ruled by King Araneae (AKA Gabriel) who is the father of Princess Heteropoda (AKA Gale).
Being one of the oldest changeling hives as well as having a militaristic culture, The Griffonstone Hive is well known for producing some of the greatest warriors the changeling species has seen, this grants them a large amount of respect from the other hives, especially the Dragon Lands who have adopted the dragons more aggressive tendencies and see members of The Griffonstone Hive as worthy opponents. This results in members of the two hive often initiating sparring matches on sight with each other.
A member of The Griffonstone Hive can be differentiated by their dark purple carapace, and orange eyes and magic aura.