Wow. Lots of questions. Applying the powder would be easy on a fresh web. Use a ketchup tube style bottle and squirt in the air above the web if it is still sticky, or just a bit
wet with dew. That should stick it nicely to the web. Or maybe a pepper shaker style canister to sprinkle it over the top.
Heat from the resin? Don't know. Have never tried that. But it sounds like a neat experiment. Webs are pretty sturdy for most types of spiders. I think it would hold up to some heat.
I used to do the hairspray thing you mentioned when I was a kid.
I love spiders and recently lost "Charlotte" my resident spider (Orb weaver, also called Banana spider). R.I.P. They only live a year and die at this time of year, but she left me a large sack of baby "goodies", so I should have more next spring. Her man friend is still living. Much smaller than her, and not a good web builder. He just hangs out in the corner of the porch. Charlotte built me a nice web on the outside of my kitchen window. I hope her kids follow suit.
You and I share the same fun with nature, I can tell.