im sure his sword is already transformed as all sealed zanpaktous are basic katanas, either ichigo doesnt know how to seal it, or it cant be sealed. also i think his original sword(the big assed one he got when he took rukias power) is also zangetsu, but remember he was forced to redesign it and increase the density of the spiritons. mmm but im not totally sold on the idea. i dont know is the sword is created from a part of the user, or if it is assigned to them in some form