I haven't had the need to repair my minis yet, but I have repaired model airplanes with polystyrene parts using 5-minute expoy. It was fine for that application, but I'd try a test spot on the mini before using it in a critical spot. I guess is that it should work just fine.Has anyone repaired the holes that ants have chewed into their polystyrene mini nucs? I have a couple that the ants have made a mess of getting the the sugar inside while trying to avoid the bees.
Epoxy resin is OK for foam. Polyester resin is not. Polyester is often referred to as fiberglass resin and is a third the price of epoxy but bad news for foam.I agree with Astrobee in that you should do a test. I would not be surprised if the epoxy melted the poly.