Scripts.img is a file archive that contains the game's scripts, and Scripts.dir is a file with info about the archive.
The script Super Mod replaces is called STimeCycle.lur, and Fight Club replaces ArcRace1.lur.
If you get an IMG tool and replace those files manually, you'll be able to have both in at once.
If you're just looking for some cheats in Fight Club there is a debug testing mode you can enable in the script if you edit and recompile it using Bully's LUA compiler.