Added A axis to XYZ mill, what can be done in AXIS?

I would expect it to be at least separated from machine HOME location first. E.g. additional parameter(s) in ini file to set up absolute or relative to HOME location coordinates of each rotational axis mounted onto machine table.

It also would be good to have similar to "Touch off" button, e.g. "Touch of work peace", "Touch off work table" or "Touch off rotary" if AXIS configured with at least one ANGULAR axis mounted onto machine table. Then work process would be next:

1. Run LinuxCNC;
2. "On" button;
3. "Home all";
4. Move tool to rotation axis and "Touch off work table";
5. "Touch off" if stock zero is the same as rotational zero
....

P.S. As far as I know, Mach3 always assume rotary axis is on the same plane as tool ZERO thus every "touch off" in Mach3 moves rotary plane to Tool ZERO location.

I think that LinuxCNC does the same as Mach in this regard, it uses relative zero, not absolute zero.

Touching-off actually calls G-code (G10) and there aren't any G-codes to set the axis position (it might be different in STEP-NC) but that doesn't mean that the user-interface can't do something different when a button is pressed.