So I have quite a few "Grab'n'Go" Windows games and programs that I've stuffed onto an external harddrive, and it is a little daunting to have all their saves end up on my C: drive. What I'm looking to do, and I hope this can be done on Windows XP at the least (if not 7 or 10), is to create a BAT file to trick each program to save their files somewhere else but C:\Documents\User\My Documents, and preferably a different folder for each program (Dungeon Siege to G:\DS_saves, RCT3 to H:\RCT3, etc).
Is such a thing possible? And is it a different command per Windows version?
You can't "trick" games while they're running, since you have no access to their code or the running threads. However, you can accomplish what you're trying to do by simply right-clicking the Documents folder, go to Properties, then Location and change the target folder. This will change the directory for Documents in your system, and your games/apps will use the new folder even if it's on a different drive.
This can be done for all system default directories, and it's very useful for SSD-based machines where space is essential.