[simulatoralive]

Personally, for a character built this way, I'd use Modular Abilities for the changeability, suitably limited to "Only for Abilities Acquired Through Limb Grafting", probably at -20%, but I don't have my books open, at the moment. Would have to be setup only for physical traits, too.

On the Injury Tolerance, add Cosmic (Works on Any Body Part) for +50%, to allow grafting anyone's limbs to yourself. You may wish to tone that down a bit, to rule out attaching robot/golem/undead/skeleton limbs.

Without an immunity to disease, however, I'd say this is an excellent way to catch anything the "donor" may have been carrying. So, the character might have to be really choosy about where those limbs come from, lest they get a terminal illness.

Also, keep in mind the Arm ST of the donor. Someone weaker than the character should give reduced Arm ST, but someone stronger would give increased Arm ST.