Indeed. Simply create another unit, which looks the way you want, and then when the appropriate cutscene kicks in, use selectPlayer to select the other unit and teleport him in/teleport out your old unit. Simple as that.
I suggest you use a custom identity, however, for the playable character, since it's not possible to 'extract' the identity information (e.g. face, voice, etc) from the "default" player character, meaning that the switched-to unit would, for instance, suddenly be named James Jamesson instead of NightJay, be black, and have a very deep voice
Good luck!
Wolfrug out.