Although I’m not a fan of glassing over rivets, I think of you wanted to do that, you should put a thin layer of cloth over the rivet line. I have some very thin fiberglass cloth, and it would not require much filler to hide the edge of the cloth edge, or the fine weave of the cloth. If you use just micro fill and sand, you will likely eventually see cracks in the paint around some of the rivets. This doesn’t mean the rivets are working. Different coefficient of expansion between the fiberglass and the aluminum rivet can cause this (I think). The layer of cloth helps to hold all this together. It’s worked for me in other areas - like fiberglass elevator fairing attach, without any cracks, and it’s held up for many years.