Is it possible to play Dead Rising 2 indefinitely?
Apart from starting new games and using them to supplement your walkthrough, as your playthrough's progress is preserved, you have the following options:
You can try using a Trainer from GameCopyWorld (not sure about the legitimacy of posting a link like that here - Steam removes them).
I'm sure there are similar more or less reputable websites out there.You can try using WeMod: it's an app that functions as a single GUI for cheats and trainers for hundreds of games, including Dead Rising 2. The website and app seem to be safe and legit.