cutting tempered glass screen protector

You can't, unless you happen to own a laser cutter.
Tried scoring with knife. Crack.
Diamond tipped engraving tool. Sort of works, but don't apply pressure as you come off the glass.
A flat diamond coated sharpening stone did remove material, but very slow
A flat diamond (tile) file was simply too coarse and caused cracking.
Do check it's glass. In true marketing style, there are plenty of 'tempered' protectors that are plastic and cut easily with a craft knife.

Lightning protection - SPD

Installed a ADEE  VAR15GT5EF T2 in a separate 2 module enclosure adjacent to the main (500mA) trip. 15kA/275V. This was partly to meet the 0.5m rule on phase wiring, and partly as there wasn't really space in the existing board.
The device is internally fused, so doesn't require a separate isolator to meet NF15-100. This does mean the supply will have to be isolated to swap it. It's wired with 16mm incoming, but the earth was just unmanageable, so that's in 10mm. 6mm minimum. The instructions show the main earth to be looped through the spare earth terminal. The thin bit of wire you can see linking the terminals (they might be linked in the potting too, but why do the job twice?) would represent a significant impedance under a overload. Earthing stayed at the earth strip. There was, in any event, not a chance of getting 2 x 16mm cables in; they would have gone into the terminals ok.
Green led is lit, and can be detected with a LDR.
Hopefully this will be enough to reduce future spikes to low levels.