Needing a craft in order to perform a meld makes sense. The craftsman is required to make or modify the gear. This is similar to repair - you need to be a crafter (of the correct level) to repair as well.
So, just like repair, provide NPCs that will do it for you for a fee. Maybe restrict those NPCs to not being able to do forbidden melds. That would make sense with the new materia compatible lore gear (which doesn't allow forbidden melds). Overmeld would be left to crafters and crafted gear.
Really, you don't want to do overmelds yourself anyway. So frustrating. Fail .... fail .... fail ...
