What I do is copy and paste back-ups of MTW: Gold once installed. I have the main game folder (which I will call the vanilla folder), with the .exe in and everything - then I have a special backup folder, with everything but the .exe copied to. You can create mod folders, and install a mod over your vanilla installation. When you want to install a new mod, just cut and paste all those files from your vanilla folder that you have already installed a mod over into it's own mod folder (leave the .exe alone). Now, copy and paste the back-up vanilla files you made earlier into the vanilla folder - and you have an unmodded game you can install a new mod over. Rinse and repeat, never having to actually install another instance of MTW: VI. You keep your vanilla files backed-up all the time, and only install mods over copies of them.