Out of idle curiosity, I’ve been playing around with these "60 minute trial version" games you can download.
I set a System Restore Point, saved the registry (File –> export…) and then installed the game. Played it for 60 minutes, let it tell me the time was up, uninstalled it, then restored back to the system restore point.
Installed the game again – it still knows its trial time is up 🙂