Like with disguise self, changelings can alter their total height by 1 foot. So they could make both their legs 1 foot shorter, and that would work. In theory, they could even turn both their legs into little stubs, with a 1-inch-tall torso, as long as they elongate their neck to be about 5 feet long.
Changelings cannot alter themselves enough to change physical sizes (i.e, changing from Medium to Small, etc). It is worth noting that while a changeling could technically shift into something like an aarakocra, their wings would be non-functional.
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.
Size. In their natural forms, changelings average between 5 to 6 feet in height, with a slender build. Your size is Medium.
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 short version is that a Changeling can shapeshift to a form that can produce sperm to impregnate someone, and can shapeshift to a form with a uterus and eggs to get pregnant, but a pregnant Changeling cannot shapechange to a form without a uterus without ending the pregnancy.
Unlike doppelgangers, which are entirely genderless, a changeling does have a default gender that manifests in adolescence, but each changeling can adapt his or her form to be of either gender, hermaphroditic (both genders simultaneously), or entirely genderless.
(2rp)Minor Flight: Changelings are able to fully use their wings at level 1.
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.
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.
Appearance. In their true form, or their form "at rest", changelings have pale skin, colorless eyes that can be completely white or completely black, and white or silver-white hair.
A changeling can eliminate or add traditional physical disfigurements - such as scars or birthmarks - when changing shape.
If the changeling has lost a limb, the limb is missing in every form they take. If they haven't lost a limb, every form they take has all the limbs the changeling normally has.
A changeling can alter its appearance. It can conceal existing scars or tattoos, or add new ones. So the tattoo will exist, but the changeling can hide it.
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.
Most often it was thought that fairies exchanged the children. In rare cases, the very elderly of the fairy people would be exchanged in the place of a human baby, so that the old fairy could live in comfort, being coddled by its human parents.
Unlike ponies, changelings do not have cutie marks. Following their metamorphosis in To Where and Back Again - Part 2, changelings have varied coat colors and insect characteristics, such as Thorax and Pharynx's horns, and they no longer have fangs or holes in their bodies.
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.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
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.
Powers & Abilities
In their human forms, the Changelings also appear to be immune to the effect of sunlight just like Stalklings, regardless if they are in their troll forms as well, thus making them the perfect spies for the Gumm-Gumms.
If you want it to be able to grow a tail when it changes into a tiefling or tabaxi, it is your choice. It is also your choice if you want the tail to be prehensile and able to grab and hold stuff. You can appear as a member of another humanoid race which will include things like tails, frills, gills, wings, horns, etc.
Changelings don't inherently recognize each other. If they don't want to be recognized then when they do something suspicious it would be an insight check against the changelings deception, which the changeling has advantage on. A changeling could have expertise in insight from divergent persona.
Conversation. By RAW changelings revert when they DIE but not when they are unconscious (it would be hard to maintain a long term masquerade if you revert when you sleep!). I bet suggested that a piece of a Changeling — such as cut hair — WILL revert, but that this is slow and may take up to 24 hours.
17. As a playable race, changelings have the following abilities: Shapechanger: Using an action they can change their appearance and voice at will, even adapting their size between small and medium in some cases.