Live-Z setting adjusted from the gcode?  

Live-Z setting adjusted from the gcode?

Hi everyone,
I often forget to change the live-Z to the correct value when changing filaments.
To avoid wrong live-Z settings on the printer, I planned to leave the printer at Live-Z=0 and to send one or more commands in the starting gcode to set the correct distance from the heatbed.

I tried now for two days, but no way worked.

I tried to use the M206 command...
M206 Z-0.20;
...and I tried to switch between relative and absolute mode:
G91;
G1 Z-0.20;
G90;

I inserted it in the start gcode section after the mesh bed level and before the intro line is printed.

It seems like the firmware doesn't accept movements of the Z axis which could lead into a "crash" of the nozzle into the heatbed.
Or maybe other commands are disabling or resetting the settings I made before.

Is there any other way to generate the "correct" live-Z from the slicer without changing the setting on the printer directly all the time and to leave live-Z at 0.000 on the printer?

Thanks,
Boby

P.S.: My settings for a great first layer are:
PLA -0.20
ABS -0.38
PETg -0.15
So, no, unfortunately they are not all the same...