Mirror adhesive OK?

As Andy Burns points out, ATMs (Amateur Telescope Makers) have been doing this for years. They specifically do it by hand because there's a significant chance of causing a hotspot in the glass if you use a power tool, which would distort the glass (they're working to sub-micrometre tolerances), and significantly increases the chance of spalling off a chunk. Just use the carborundum, by hand. It's no more time-consuming than honing the edge of a scythe.

You buy a new pane of glass and have the edges ground by the supplier. Cheaper and easier all round.

I have a proper wet-disc diamond grinder for doing stained glass work. For cheap mirror glass (under =A350/ m^2 is cheap for the sort of glass I use this thing on) I'd get the glazier to do it on their big belt machine.