The "Offline NT password recovery" program (which is actually a Linux floppy) contains a basic registry editor. Google for it.

It's not very easy to use, but you can make certain modifications (it's mainly used to modify the SAM to change the admin password if you've forgotten it)

It's text-based and starts by asking you a series of questions. The registry navigator is (iirc) command-line driven, with maybe commands like "ls" and "cd"

Dunno if it works on XP home though, it's intended for NT and NT-based systems (maybe Win2k, XP pro) - you can give it a go.