if you're going to back up anything, take a back-up of the ENTIRE game (all folders - though the DL folder isn't neccessary to backup, exept if you're going to uninstall a game). Only backuping the neighbourhood folder won't help, because there's other files that are modifyed every time you play than the ones you find there.
and what exactly were you trying to modify? might help...
and the best thing is to install the games in the same order that you did the first time, if you're using a backup (I think), or things might go wrong when you try installing it over again. I always save a backup of the latest games and use that when I'm starting over, so I only have to uninstall/install one game. (backup dl folder and other things, uninstall game, put in backup of all games up to the new, install game again, and play

). but I have to say that I usually start over again on a new game when I'm installing a new EP.