Open the screen in screen4 (or MachScreen if you prefer) double click on the button and change it to a VB button then save as a different name (so it doesnt get overwritten if you upgrade) and then in Mach load the renamed screen. Remember you need to make sure its saved a a .lset.
Regarding the home switch on the turret, you dont actually need one, just need to make sure when you home the turret is on tool 1.
Actually thinking about it as you are working in G54 coords homing would not really be needed if you put an A DRO on the screen as you could just zero by typing. Probably still best to home though but.....
Hood