Are Xbox One and Xbox One S controller faceplates interchangable

Depends on how much you care about the warranty and if both controllers use the same faceplate and cosmetic parts. If it will work and you care about keeping the warranty, use a skin. If you don’t care (or it’s the 90 day warranty that isn’t worth preserving if you can do the work yourself), then it can be done.

You will need to damage the identifying label (which will reduce the resale of the controller) and make it harder to sell later on to normal buyers (technically capable buyers probably won’t care) so you need to decide if the resale loss and voided warranty are worth having that faceplate.