What I would do is take a mag that doesn't click into place, hold it in the magwell and see if it works properly with you holding it. If it does, then I would just make the small square hole in the side of the magazine slightly taller to mesh with the mag catch, rather than mess with the top of a working mag. Less things to go wrong that way I would think. Just do it carefully and slowly, cause if you make the hole too tall, the mag will be loose and may not feed properly.
