Just got a P225A1 and I'm trying to reverse the mag catch, but it's different than the P220, P226.

From internet searches, I have read that is like the P224, where you push in the release, and stick a small punch or paperclip in the hole that is exposed on the other side.

I tried this but I can't seem to get anything to "remove".

Anyone know how this is supposed to work?

It sounds similar to the SP2022. See this photo:

MagCatchRelease by GaryBF, on Flickr

Yeah, seems similar. When I push a small punch or paperclip in the hole, I can feel something with a a little spring to it, but the locking piece doesn't come out. I can actually see the locking piece moving further inward.

Do you have to pull on the groove in the side of the plastic locking piece to get it out?

As I recall, it is all plastic and no springs, so yes.