You can have the 3D bits be different, but the texture painted on the model will have to be the same.
As I said, there’s two components to an armor piece. Only one of those components is a problem.
To illustrate, I loaded the ToV Mail Gloves into the Wowhead Dressing Room as a Human and a Vrykul. The Human has the 3D bits, but Blizzard never made the 3D version for Vrykuls so they don’t have them.
As you can see, when the 3D bits are removed, the texture underneath is the same.