It's scary to imagine that there are people out there, that can perfectly copy the appearance of anybody. They could impersonate your neighbour, your friend, even your family - and you might never know. They are incredibly hard to detect, and any single one of them is a danger to our society.
Changelings are a humanoid species with the unique ability to adapt their appearance at will. This shape changing ability is not just simple illusion magic, but a physical transformation of their bodies. This makes them very effective actors, spies and criminals, which has led to a lot of distrusts against them all over the world. Because of that, many changelings decide to hide their heritage, completely blending into the culture around them.
Description

Changeling by Satrium with Portrait Works
While changelings can look like anyone, they also have a true form. Their natural appearance often looks rather nondescript, like an unfinished painting. Their skin is pale, either white or light gray, and their hair is thin, most commonly in a shade of silver-white or platinum. Otherwise, they have little, if any, body and facial hair. Their eyes are usually colorless or blank white, often appearing sunken and circled by dark rings. To many, this makes them seem expressionless, almost featureless and nearly indistinguishable from each other.
However, most changelings are rarely seen in their true form, preferring to adopt all kinds of humanoid shapes instead. A changeling usually has a handful of preferred appearances, and often even a feature - like a birthmark or the eye color - they tend to maintain across their appearances.
Abilities
Shape Changing
Changelings have the magical ability to change their appearance at will. For most of them, it is easiest to copy the appearance of another humanoid completely. This ability is magical in nature and always produces a perfect mirror image of the target. From there, many changelings are able to adapt various aspects of their form, like facial features, skin coloration, eye color, hair length and color, and voice. During their transformation, their height can change by up to 0.5m, and their weight by up to 50 kg in both directions. It only takes a couple seconds for a changeling to adapt their new form and they can do so as often as they like. The new appearance lasts until they change again or die.
With a lot of training and self discipline, some changelings can improve their shapeshifting further, and develop extraordinary abilities. These abilities can range from copying unique traits - like breathing underwater or flight - to even completely liquifying their anatomy to avoid serious injury.
While a changeling’s disguise is nearly perfect and almost impenetrable, this is only because people tend to miss the subtle clues that should make them suspicious. Changelings can replicate the appearance of a person, but never their belongings or memories. An imposter therefore, might lack the skills of their alleged profession or species, seem unfamiliar with their apparent culture, or otherwise act differently than the person they are impersonating.
Insight and Healing
Being able to nearly perfectly copy the physiology of an individual they have met in the past, changelings have an instinctive feeling for the people around them - especially their physical features and appearance. This allows them to read body language with astonishing accuracy. It also gives them a sense of the physical well-being of another person, making them great at detecting and treating injuries and illnesses.
Culture & Philosophy
People fear what we can do, and who could blame them? Our abilities allow us to infiltrate and deceive, impersonating their loved ones or taking advantage of them in all kinds of ways. While there are a few that do abuse their abilities like that, many of us just want to live, and often that's just easier by hiding what we are. People fear the unknown, and fear brings them to do horrible things. Staying out of sight is the safest place for people like me.
— Nix

Changeling by Satrium with Portrait Works
Changelings are not well received in many places around the world, their abilities leading to an inherent mistrust by other people. Because of that, many live in secret amongst others, blending in and living in their shadow, often embracing the anonymity of a big city.
Their ability to shape-change gives changelings a unique perspective on things many other species take for granted, like individuality, gender, appearance, and a sense of self. To cope with these questions in the light of their ever shifting nature, changelings developed various schools of thought, cultures and philosophies. In essence, these philosophies can be split into four groups.
Adopters
Adopters suppress their shape changing abilities, and live life in only one form. They fully embrace the culture and people around them and give up their changeling nature entirely. For all intents and purposes, they become a part of their surroundings, ethnicity and culture with no intention to ever reveal their nature to anyone around them. Some seemingly even forget what they truly are.
Travelers
Travelers live in a singular place for a limited time. They build a persona, with the intention of moving on in a couple months or years. But for this time, they fully become that persona, embracing the culture and traditions of their surroundings, living a normal life. Over time, they become restless, sometimes out of fear of being detected, other times not shifting makes them feel locked in. So at some point, they decide to leave their life behind and move on to the next.
Shifters
Shifters embrace their changeling nature and possess many different shapes and often different identities and lives all together. In their belief, they are both who they are and who they seem to be. They take the concept of a dual life to another level, and some will successfully live as several people for many years. Some shifters even come together in small communities, sharing the lives and personalities of multiple identities between them. They often no longer have a sense of true self, but become a part of a collective society, working together towards a shared goal.
Trueists
Trueists prefer to live their life in their natural form and to live in a community of fellow changelings. To them, appearance becomes secondary and morphs into an abstract concept. For some, the transformation of the body becomes a spiritual or mystical act, while others completely embrace it, freely morphing their appearance for fun or expression. They often pursue an abstract concept of perfection of the mind and body. These kinds of changeling communities are incredibly rare, and often hidden in remote places.
I love the various ways you thought of how someone like a changeling may handle their circumstances! Love to read further on their cultural groups when you get to them
Thank you! I already wrote a tiny bit of a cultural changeling group here, and there are many more to come. Glad you liked it!