*Please talk to your DM when presenting a Homebrew race*
I have the document on how this variation of changeling works but basically Changelings are a type of half breed that is half Doppleganger as the father and another race as the mother. When it comes to changing forms think of how water pours in a short glass and tall glass; they can change form but they can't change mass. The changeling mass is determined by the mother's race for example this Rhodes; he is half dwarf so he could become a really skinny and light half elf or a really dense goblin.
Like all changelings they have no body hair and have a pair of horns which are present in all forms.