It's an unnecessary device that was put in at the insistance of FN when JM went to them to have the HP built. It serves no purpose and I've seen several postings here and elsewhere that indicate there have been zero instances where removing it made a lick of difference in court.
Now, take the slide off and have no mag in the frame. There's a wee pin in the side of the trigger. Bash it out. This will allow the mag safety and its spring to come out the back of the trigger in the frame. That's all there is to it. Your trigger pull has dropped considerably and in most cases your mags will drop out with their own weight. Clean up the sear and hammer interface, change the rest of the springs and you're set.
Don't spend a lot of time hunting for Inglis mags. There aren't many about. The CF issue Inglis HP has never, I say again, never, been released by the Canadian government for sale to civilians. Including mine.