GEM can actually "exist" for every game you install it in. Even though some of them are someway monitored (online games usually) and may crash when they detect an external app running over it.
Yes, it works perfectly fine with Attila, Warhammer and possibly every Total War, bar Arena (online game, sigh).
This link comes from the GEMFX Thread:
http://www.mediafire.com/file/7qftns...EMFXv1_0_9.exe
Simply run the installer and point out the location of your game's folder (must be the one where the .exe" file is). Then you can run the "GEMFX_Configurator.exe" from that folder and start tweaking it. It also works while the game is running so you can see the results in real time which is great.
With Attila I have "Compatibility Mode" ticked, but I can't remember whether it's necessary or not for it to work.