parts size change?

An idea occurred to me involving the idea of changing the size of a particular part from one figure scale to fit another. Personaly I have no clue how something like that could be accomplished, but I have seen the parts casting tutorial on Sector70, so I wondered if there was some other casting method that would allow said cast to be shrunk or expanded?
My apologies if the idea is beyond impossible for anyone to come up with an answer for it, but I figured I'd throw it out there and see what you guys thought.
My apologies if the idea is beyond impossible for anyone to come up with an answer for it, but I figured I'd throw it out there and see what you guys thought.