You can appear as a member of another humanoid race which will include things like tails, frills, gills, wings, horns, etc. However, your stats do not change so you cannot use the tail prehensively, cannot breathe underwater with the gills and cannot fly with the wings.
The true form of a changeling is a bit paler than a typical human with slightly elongated limbs. Their eyes are colorless and ringed by black as pictured in the artwork above by Julia Zhuravleva. They have no body hair, but the hair on their head can be platinum, white, or silver.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
A common way that a changeling could identify itself is through displaying unusual behaviour when it thinks it is alone, such as jumping about, dancing or playing an instrument – though this last example is found only within Irish and Scottish legend.
As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
They have large colorless eyes circled by thick black rings. Their hair color is most commonly a light shade of silver followed by platinum and blonde. In rarer cases, their hair can be pale shades of green, pink, and blue. Similar to elves, changelings lack body and facial hair.
Within this description there are variants of changelings that show subtle differences. Some have opalescence in their skin (as if it contains various colors instead of just being white) and their eyes can be completely black.
Are they biologically asexual and just choose their current sex with shapeshifting? Yes. What's been stated in the past is that changelings set their sex with shapeshifting.
Changelings have red blood like a majority of the other races. Bleeding around others may alert many that the Changeling is not of the same race (should the blood color vary). For this reason, a Changeling will usually choose to take the form of a race with red blood.
Changelings typically have large eyes with narrow pupils, ranging in color from white, to yellow, to black. Hair colors are similar: Light grey, platinum blonde, shades of silver, all the way to the darkest hair color being a light brown.
Changeling Reproduction
If a changeling with the Racial Emulation feat matches its subtype to that of a partner, a child resulting from the union will always be of that humanoid subtype. If a changeling in a female form conceives a child, she loses the ability to change her gender until after the child is born.
Languages: You can speak, read, and write Common and two other languages of your choice.
A changeling can't make the wings at all. If they had wings, like from a class feature or something, then they could look like an Aaracokra with wings because they will have those limbs at that point.
Changelings are largely equine in appearance but possess insect-like characteristics. Originally, they had black carapace-like coats, webbed manes and tails, blue reflection-less eyes (unlike their queen's), fangs, bent horns, jagged ears, insect-like wings, and holes in their legs.
Most changelings don't know they're changelings.
Though they may always feel somewhat different or removed from human life, most changelings are too young to understand who they truly are.
Powers and abilities
Shapeshifting – Changelings can appear human, and are capable of shifting between forms in order to feed. Sharp teeth – Changelings have a lamprey-like mouth covered in sharp teeth that allow them to feed on humans.
Changelings have the unique ability to transform their body to look however they want, provided they keep the same arrangement of limbs they already possess. It is very rare to actually see a changeling in it's 'true' appearance. Even when disguised, changelings can instinctively recognize each other.
A changeling can eliminate or add traditional physical disfigurements - such as scars or birthmarks - when changing shape.
Changelings have an interesting relationship with gender as a concept, which is probably part of the reason a lot of the art doesn't find it necessary to distinguish the males with facial hair. As they're changelings though, they can have any kind of hair they want.
Changeling Traits
Age: Changelings reach adulthood at the age of 16. Their fey heritage allows them to live much longer than humans, up to 200 years.
Changelings are humanoid creatures with discolored, slimy skin, hollow eyes, and a round mouth with many teeth. They can appear human, but their true nature is revealed in their reflection.
Age. Changelings mature slightly faster than humans but share a similar lifespan—typically a century or less. While a changeling can transform to conceal their age, the effects of aging affect them similarly to humans.
The Changeling's Shapechanger trait states: As an action, you can change your appearance and your voice. You determine the specifics of the changes, including your coloration, hair length, and sex. You can also adjust your height and weight, but not so much that your size changes.
It's not widely known, but one of the few ways one may determine that a person is, in fact, a changeling has to do with their hands. Changelings generally do not have the skill to replicate "life lines," and sometimes even fingerprints.
Will a legless changeling regrow both legs when it copies someone? I say no. The changeling can change their coloration, hair length, sex, height, and weight, but they can't change their number, arrangement, or function of their limbs, because nothing in the feature says they can or even hints at it.