I'm not sure what all came with the Plat edition, but I'm assuming it was just some "exclusive" DLC, book, etc. with the actual disc content being the same as the regular version. If this is the case I would think (but could be wrong) that you could simply buy a U.S. version disc of the game, and you could get all you downloaded into your game.
Anybody know if this would work for Rodger777?
(although if he does this, he might not be able to use the DLC that came with the Plat. edition)
I am not certain, but I don't think GT would load the game save from a different region.
Most likely not. Not positive about GT5, but I know Little Big Planet wont.