All purchases of HP15c include a screwless back door until 2024.1.15

A rendering of the Aviation Overlay:

Labels above the number keys are reached with GSB number. So, Cº->Fº is reached with GSB 7

Labels in the angled part of keys are reached with GSB .number. So, Mach->Tas is reached with GSB .7

This will be the method for all Software Pac overlays going forward.