I was watching this video, and the guy says if it has the pin, you have to drill it out if you want to keep the sight for later use.
But then he says it's not a problem if you don't want to keep it, just drift it out, and the pin will shear off. Seems to me you can shear it off and drill it later, though it's probably easier to drill it while still on the slide. Before I do any drilling, I want to make sure I understand it right.