Changelings can match the sound of someone's voice (including their accent), but not their mannerisms or behavioural idosyncracies, and mimicing someone convincingly may require both. The relevant text for the ability is: As an action, you can change your appearance and your voice.
Changeling Instincts: You gain proficiency with two of the following skills of your choice: Deception, Insight, Intimidation, and Persuasion. Languages: You can speak, read, and write Common and two other languages of your choice.
according to the rukles for changelings: Languages: Changelings begin play speaking the primary language of their host society and Common. Changelings who have high Intelligence scores can choose from among the following bonus languages: Aklo, Draconic, Dwarven, Elven, Giant, Gnoll, Goblin, and Orc.
5e Racial Stats
Speed: Changelings have a base speed of 30ft. Languages: You can speak, read, and write Common and Sylvan.
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.
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.
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.
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.
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.
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.
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.
Changelings born from two changeling parents are born in their natural form: pale, slender, with colorless eyes and white hair.
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.
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.
Changelings are a species of elf-like demons with pale skin and pointy ears. They are connected to the forests in which they dwell. Changelings are known to place their young in the homes of mortals so they can grow up in safety.
As for being tattooed, changelings can definitely be tattooed, and they can just as easily erase the tattoo with a moment's thought.
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 able to change their form at will without expending a spell slot or using a disguise kit, but there are limitations to their abilities. For instance, they cannot change the clothing or equipment that they are wearing. Whatever they were wearing as their previous form will carry over to their new one.
Changeling blood is green, unlike most other animals. Changelings, despite their thinly and seemingly fragile frame, are capable of surviving otherwise fatal injuries thanks to their magical abilities.
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.
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.
Unlike ponies, changelings do not have cutie marks.
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.