It's permanent but honestly, after thinking about it I'm not so sure why we made /modname and /modsecid one-time only under level 20, it would make more sense if it's unlimited before 20, but after that you just can't use it at all.
Best thing to do for now would be to remake (since I assume you're still under 20); should be able to get back up to where you were pretty fast. For the record I can't change it directly. :P