How about this. Delete the end folder from your server files. Go into the Gregtech config and disable generation of ALL ores that are in the End. (sodalite, olivine, tungstate, sheldonite). Disable the dragon egg power siphon. Now you can freely let your players go to the End, since there is nothing there that will benefit them more than normal.
I know how to do that and fix it. I just choose to take the challenge