I mentioned my thoughts on slayer with the gamemode system a while back - You could create a gamemode generator system with Slayer, where you plug in all the settings, pick a save, add-ons, and environment settings, and it builds a gamemode folder add-on that appears in the list. Selecting it would load Slayer, the base gamemode, then any other dependencies. Perhaps required add-ons could be detected automatically using the build and slayer settings. Any changes made through Slayer while this gamemode is running could be stored in that same file (unless the person has turned into a zip to release it or something, in which case it wouldn't save).