AFRANK: It is rigid if you mean you might move it.
That is why I said to use care. Take your time. You will not screw up anything if you are gentle and take your time. Again, the mirror is rigid and fits into a slot. As far as removing the reflective silver surface: mere water with a tiny bit of soap will not ruin the silver surface of the mirror. Alcohol or, perhaps, lighter fluid, will.
Lukas_87 is correct in that removal of the silver would remove the shadow image which confirms focus. - David Lyga