Moving .app Games to External Hard drive

I have searched the forum and couldnt find anything about this, however i am sorry if this has been covered. I was wondering if i was to reformat my Mac would it be possible to move my .app games to an external hard drive and NOT loose the saves. i.e. COD Black Ops, if i was to move this to an external hard drive and wipe my Mac hard drive then reinstall OS then transfer back across Black Ops would it still have my multiplayer level and game saves etc. i know .app files are self contained

Instead of doing it that way, use Time Machine to make a backup of the entire hard drive and either restore everything after the reinstall, or selectively reinstall your game data and anything you wish.