Q Originally posted by Yago Aginor How functional are the changes to sex(gender) introduced by a changeling's changing ability?
A Absolute. A changeling's gender is its default that it will revert to if it, for example, dies. But a "male" changeling could actually assume a female form, become pregnant, and carry a child to term (it loses the ability to shift gender while pregnant). This will be covered in more detail in Races of Eberron.
Would Var's voice change enough for him to safely pass for a girl?
He'd get a -2 to his Disguise check, but that's what the +10 bonus is there to offset. Yes, change in voice is part of the transformation.