The taller 10 round or less mags for restricted states are supposed to be made so that a person can not modify them to hold more rounds if my memory serves me correctly. I took apart a couple Baretta mags from the 94 AWB days. They were filled in so that one could not make them hold more by changing a couple of parts out. The AR mags I saw like that were solid in the bottom as well.
It may different now for all I know.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.