Mach3 has been designed to slave;
X axis to either A, B, C
Y axis to either A, B, C
Z axis to either A, B, C
And without duplication of any slaved axis.
You can slave up to 3 pairs of motors and obviously you can call these motors any axis you choose (without duplication) but to make sense of any key presses or screen DRO’s you would use one of the available Screen Designers to modify your screen to change the X, Y, Z axes DRO’s description to your own choice (deleting the A or 4 axis DRO as this will not be operational if you slave any axis to A).
Tweakie.