Hm, you should only need to back up your Epic (Mega)Games registry settings. Use regedit, go to the Epic (Mega)Games key, and select it. Then select Files, Export, and type in a name for your .reg file. You should now have backed up your registry settings and are free to delete the existing ones. If something does go wrong (it really shouldn't), you can just use the newly created xxx.reg file (xxx for the name you gave it ... I recommend xxx in order to lessen confusion) to restore all your keys.