I haven't figured out how that works, there must be some workarounds applies and the only thing it should take from registry is the default path for Unreal. Also you can't install the Unrealgold patch over the normal Unreal versions. Even though when I copied the system dir from unrealgold I couldn't use separate tree, I had to install it right into my original unrealgold directory, it failed otherwise. I did backup the files though. But this was real inconvience. If I knew what files it looked for or what system it uses I could work around that, but this was inconvient when you want to run separate system trees and stuff.