I don't know about plaster for drywall, but get out a hunk of cardboard for a practice board, your plaster, and whatever tools you have, and see what you can do on the board. If that looks promising, have a go at one of the angels.
But really, death is sacred, too. If it were me, I'd paint the haloes to suit the subject matter. I love the barbed wire idea, and it'd be easy to paint with your 18/0 round brush.
Hee, Precious Death. I want to see pictures when they're done!