I thought a rotary Dremel tool might work. That is how I put the bevel in originally and then freshened it up as needed.
To grind off a turned down edge, use a smooth ceramic floor tile as a lapping surface and paint on it a very thinly a slurry of lapping powder (3 to 5 millimicrons in particle size) and water, then invert the mirror, place it carefully on the wet powder, and slowly begin to move the mirror in a W fashion as you slowly rotate the mirror about it's axis.
This will quickly put a narrow "flat lip" on the edge of your mirror, removing the TDE. Afterwards, use a very fine diamond file and some water to put a small bevel on the edge to to prevent chipping.
Don't be aggressive and overdo it; the lip forms very quickly.
The lip can be 2-3 mm wide. depending on the extent of TDE. The 45-degree fine bevel can be as small as 1 to 1.5 mm.
Anything rougher than the finest lapping powder will leave a jagged border on the polished surface.
PS But if Dremel tool works that's fine with me, as long as the polished surface is not damaged.
Edited by MKV, 11 April 2021 - 10:12 PM.