I've had more than my fair share of experience removing concrete from things that aren't supposed to have concrete on them. I thought I'd share my thoughts:
-Concrete will damage glass, but it takes weeks.
-Lightly tapping with the rubber mallet will work incredibly well, but it will leave a dullish residue where the concrete was. You may be able to remove the residue with a cloth, or with the acid (but be very careful!).
-Be careful with muriatic acid-make sure you follow the dilution instructions carefully, and keep water handy for rinse-off. Muriatic acid will attack uncoated metal (but it takes a while). The clear coat may protect you a bit longer, but still move quickly. I'd recommend diluting the acid down, trying it, and if it doesn't work, slightly increase the concentration and try again.
-After applying and rinsing off the acid, open the door and rinse off any liquid that got trapped in the door jam. This will prevent any acid that was trapped there from chewing stuff up.
-Gas mask is overkill, but do it outdoors-the fumes are pretty harsh.
I think the recommendation to test on a junk car is the best possible advice here.