I'm sure i can't be the only person who has had to remove a mirror stuck on with epoxy, or relocate it on a mount after a bit of fiddling. In the past I'd used an old soldering iron tip and then a thin blade to lever them off, but have had a few breakages like this.
Today I tried using a blow torch on the rear of the mount (holding the mount in something that isn't going to transmit the heat to my hand!!) The mirrors literally just fell off!!
Very easy, mounts are unmarked and the glue residue is easy to deal with if you do it during the cooling down phase.