hi , man! :)
here a Steam L4D2 forum link, for an interesting add-on that allow to get back all Mutation mods cycled off, (as the near last "Gib fest", that one with M60-infinite ammo) either Valves's ones or comunity-developed ones http://forums.steampowered.com/forums/showthread.php?t=1529433
see you soon! :)