Isn't it annoying when you get a trophy you already have in the lottery. Here's how to make sure it never happens again.

First back up your save game file. Then go into the lottery window. The game will save. Now pull out your memory card and put in the coin. If the trophy is not new, put back in the memory card and reset. You will still have all your coins and the old trophy will not be there. When it asks you to load the game press yes.

If it is new, put back in the memory card, exit lottery and overwrite save. There, guaranteed new trophy!