You can order new rivets from trimtags.com that look exactly as original. I removed my tag from my X44 car, stripped and repainted the entire firewall, and simply re-installed the tag with the replacement rivets. No problems and still look factory.
Of course, I had a nice X77D80 tag made up and I am currently selling the car for well over six figures on ebay as an unrestored all original Camaro and see no problem in this, since it is apparent that I did such a great job in installing the new rivets, no one can tell. (Yes, I'm kidding about this part...but you can get original rivets if you want them to look proper)