I always understood that it was riveted in place. So you have to file the rivet... and rivets a new one when mounting it back. Not very convenient for the amateur - and not necessary unless the CP is damaged.
I was afraid they were rivets. No way I'm going to mess with them in that case. But I had a closer look, and the left one is not a rivet at all, I could pull it out with my fingernails. But I cried victory too early, the right one could not even be driven out, so I'm no further. A strange combination though.
They are not exactly rivets, as I understand they are pins that are pressed in place. I believe that a special tool made of hardened steel is inserted in the magazine well, then the pins are pressed from each side by a vice. This make the pin expand and stay put. I once saw one of these tools on ebay, but didn't know what it was at the time, now I wish I would of bid on it. It's not a very good design and I am not surprised if one of yours is loose, but not to worry as it is held in place by other things. If you don't have a tool and new pins, don't take it out!