Changelings are a humanoid race who are distantly descended from doppelgangers and share their shapeshifting qualities. Their shapeshifting has led to them being used as spies and assassins which has, in turn, led to them being mistrusted amongst the people of Khorvaire. Changelings are subtle shapeshifters capable of disguising their appearance, making them consummate spies and criminals.

Rules page on Eberron Pathfinder.

Culture (taken from Keith Baker’s Dragonmark blog post on Changelings)

There are three primary changeling cultures in Khorvaire.

• Foundlings are changelings raised by other species. This could be due to interspecies romance, or the child could be orphaned or descended from an outcast… or part of a family of foundlings. Foundlings have no knowledge of changeling cultural traditions, and rarely have contact with changelings outside their own families. Foundlings develop a wide variety of philosophies. Some foundlings hide from their true nature, adopting a single face and never changing. Some are sociopaths who prey on those around them, stealing the faces of those they kill. There’s no predicting the beliefs of a foundling, and they can be found anywhere.

• Stable changelings live in changeling communities that are recognized and known to the people around them. They are often comfortable wearing the skins they were born in, feeling no need to hide their changeling nature. In the Five Nations, Breland is the only nation with stable changeling communities; other stable communities include Lost in Droaam and the Gray Tide principality in Lhazaar. Stable communities were founded by tribal changelings, so some traditions overlap; however, many have been abandoned as the members of the community don’t feel threatened.

• Tribal changelings cling to traditions stretching back to their origins in Sarlona; they refer to themselves as ‘The Children’. Their culture is defined by the hostility and distrust of outsiders; they hide their communities and their true identities from others, revealing just enough to keep strangers from seeking more. They live in the shadows of the other races, using their wits and their gifts to survive. Most tribal changelings spend their lives in motion, traveling from place to place and never staying long enough to draw unwanted attention. They are seen as tricksters and tinkers, and this reputation is often deserved; tribal changelings don’t consider it a crime to deceive single-skins. The tribes are based in Thrane, Aundair, and Karrnath, but wandering tribals can be found across Khorvaire.

One of the pillars of tribal culture is the idea of Personas: distinct identities that serve a personal and cultural role. Personas are tools. They have established identities that can be useful to the changelings who use them; for example, a given shared persona may have connections in the Boromar Clan established before the PC was born, and the persona provides them with access to those contacts.

It is also a way for the changeling to focus their thoughts and talents. Personas are more than just faces. Mastering a persona is like learning to think in another language. It’s about being that person. One persona may be soft hearted and dislike violence while another is a ruthless killer. So when she knows violence is around the corner, the PC will give way to the killer and let him handle the fight. Conversely, the other persona knows people and is good at friendly manipulation; she’s the persona the PC uses when she plans to rely on Deception and Insight, while relying on the killer persona to perform Intimidation. From a mechanical perspective, the rogue PC has the rogue’s specialization in different skills. From a story perspective, that specialization reflects her personas.

Every changeling can assume any number of faces. As noted above, some faces are newborns with no history, no fixed behavior; you might use them once and forget about them. Each changeling creates their own personas, creating one or more people they want to be. Not every face a changeling assumes is a persona. A tribal changeling can impersonate a guard for a momentary advantage and then throw the face away, or wear a particular guise for a party.

But they can also inherit personas from other members of their tribe. This involves training, with a living master of the persona teaching the youth how to be that persona. Many personas are unique, with only one member of the tribe being allowed to use the persona at any time; this prevents someone from doing something with the persona that could spoil it for others. However, there are also personas shared by the tribe. These are generally travelers – merchants, bards, tinkers, mercenaries – people no one knows exceptionally well, so it’s easy for different changelings to play the part without getting tripped up by recent events.

A second concept for tribal changelings is the ideas of skin cant. This is the concept that tribes employ cosmetic details – tattoos, birthmarks, scars, patterns of freckles – that have specific meaning to other members of their tribe. A particular facial scar (which could be added to any guise) might tell other members of the tribe I need help or everything I’m saying is a lie. It’s a simple way for a changeling to share information that also allows members of a tribe of identify one another even if they are wearing unknown faces.