I posted a how-to on this a while back. Might wanna search for it. I go through all the steps involved.

Peening is the way to go. The trick to it is to put a small socket behind the jaw to take the force of the blows. Don't let the plastic absorb any energy.

I don't see any advantage to using a pop-rivet. For one, you create a few extra steps, you get a joint that isn't as strong, and you still have to drill it out when you replace it anyhow.

The important thing to remember when doing this job is to not widen out the hole in the regulator arm when you drill out the old jaw. If you make that hole too large, the new jaw will be loose.

-tp