That's completely true. I've already been testing which cameras I have and what software I should use to get this to look good. Although I may be able to pull a george lucas and just slap his head on the original body for some scenes. Also a lot of the scenes with Anakin are close up shots so I may be able to pull it off a lot easier (note that I am only replacing the kid anakin).
EDIT: nope, it will indeed not be working as planned, you called it ;-)