I have an exterior steel door (actually wood steel clad) that has the outer IGU pane broken out. The interior trim around the glass is plastic and has what appears to be round plastic filler plugs, maybe 5/16" diameter spaced about nine inches apart. Are these round filler plugs covering screw heads that allow the trim to be removed for IGU replacement?

Yes.

Agreed, pick them out with a wire brad or point of a pocket knife.

Agreed, pick them out with a wire brad or point of a pocket knife.So, it sounds like they're not bonded in, do they look pretty tight. Thanks for your help. ;)

Usually not glued in, just pressed in. Pry around the edges with a knife point.