Procedure to decrypt and backup GamersGate Game Setup Files:
If I didn't explain this well, here's another guide (on GOG of all places):
Yes you can! You need to be able to log into your account to download the files, though, so I would suggest doing so as soon as possible. Once you have downloaded the files, you need to click "install" but DO NOT ACTUALLY INSTALL THE GAME -- merely leave the installer active. This will de-encrypt the setup file and keep it de-encrypted (once you install the game, it re-encrypts the setup file and renames it to something like "launcher"). All you have to do now is copy the entire downloaded folder to a new directory (i.e. on an external hard drive) and voila! Instant backup for your install files with no need to log into anything. I've done this with about 30 games that I've downloaded through GamersGate and have never had an issue with it.
EDIT: Ah, Walkonshadows beat me to it.
Thanks, this is extremely helpful!