You cant put the identity of one shell to other, if the rs shell is beyond repair id strip the shell of any good bits and scrap it and go looking for a genuine shell that needs all the bits you have, i know thats easier said than done. Or you could make an RS Turbo replica with the donor shell but you'd need keep original vin etc of the donor shell and it will never be a genuine RS..
But no i wouldn't change identity of the shell.