Slow your roll dude.. no one was a jerk and if anything, I gave him a great idea to do it legal AND get magazines he could use out of his state later if he wanted. But you blew that off, so chill. It's amazing how up tight some people are around here. AND, what I said is true... in the end, it is on him to know for sure and feel comfortable with what he does.
Now.. you need to do some research on "permanent" as nothing is "permanent". Nothing... pins, epoxy, rivets, nothing. So, often, "permanent" simply means you need to use a "tool" to undo the mod. So, in this case, you need a "tool" to remove the floor plate so the argument can and has been made that in fact is "permanent" once the floor plate is put into place.
Think about this, your own logic is undone by the way the mag legally came from the factory.. his mag came "permanently" limited with a pin. A pin you can take out with a tool - in seconds. So much for "permanent" huh?
So in my example, legally take them apart into kits. Remove the pin. Get legal 10 round blocks. Put back into working order. Floor plate now is in place and a tool is needed to remove the floor plate.