I was wondering are friend codes that are for games, different for each disc of the same game? Or does the wii generate a friend code for the game and "remember" it no matter which disc of the game is used?
Asking because of renting games and deciding to go and buy that same game...will that games FC change?
No, once a Friend Code is established, any disk retains the exact same one. The friend code is actually part of a game's saved data once you register it, so as long as you don't delete your save data, you'll have the same Friend Code. You've nothing to fear in renting one game and then buying another.