OK, I think I got it. I had to edit the modchooser.ini file (blanking the SGO6 mod), copied over the entire dir tree in OP with OP+4 mod, and deleting the mod folder which contains SGO6 from modchoosers backups and replacing it with a blank dir tree from an open slot. Seems to work again, and even reinstalled SGO6 into modchooser and selected the mod.