I wondered if I would be the only one with this problem.
Couldn't get either phillips head screws loose, even with penetrating spray, heat, etc. Finally got the passenger side screw to move and removed it about 1/4 turn at a time. Driver's side never would break loose.
The good news is, that after applying heat (wife's hair dryer) to the driver's side assembly (warmed up the whole border portion of the mirror), I could "gently" remove the mirror after pealing the frame from around the mirror edge. The mastic holding the original mirror in was soft and removal was easy once the border was pealed back. Best to wear gloves in this operation, just in case something breaks.
Putting the new mirror in was sort of reverse of removal (as the repair manual says). I cut some small pieces of the supplied double sided foam tape and placed them on the pads on the mount frame. Then, I warmed the whole thing up again so the mirror border was pliable and soft and gently pressed the new lense into it's new home. I used one of the wife's wooden fingernail cuticle push-back thingies as a "coaxer" aroung the plastic frame to coax everything into place. No worries about the new glass falling out. Nice & snug.
This is without doubt one of the best low $$ upgrades you can do. I've always been paranoid about anybody that may be hanging back in the very large blind spot these cars have. No more.
Great upgrade. Thanks to all who contributed to this thread.