It is an asphalt product, even smells like roofing tar. If it were super frozen with dry ice, it might work. But at room temperature it will just put a bunch of dimples in it.
Use a plumber's torch, heat small areas about 4x4 inches, keep the torch about 6-8 inches away so it doesn't catch fire and only until soft, about 5 seconds, then scrape with a putty knife. You want it soft like clay and it comes off nice and clean (mostly). If it is too hot it will melt. It will still come off but will be messy. A few seconds to cool and you're back in good shape.
I don't know. Looks like they scuffed it with 80 grit on a DA. A bunch of factory paint came up with the liner. They did do a lot of short cuts, however. Like lining over rust. The bed has dozens of holes from self drilling screws, and they just put masking tape over them and sprayed. Didn't remove any dents on the floor, either.
Listening to this sounds like any thin paint would be never found. As expected. I suppose my biggest thought is Toyota never sending out bare metal on production of these machines.