Question about spellcasters and un-learning spells

Yeah I don't think you can although I wish you could.
I had to remove my sims from a Spellcaster club because I hated how they kept casting spells I didn't want them to and e.g. got rid of curses I didn't want them to get rid of and fiddling with their transportation settings. Though I guess you can rather easily add the curses back with cheats but still. Ivan also managed to create a permanent clone during a club gathering I wasn't controlling though I kinda loved it and now refuse to use the spell again in case he disappears.