HIYA Ger, I have never been able to pull ANY of those Vars listed in teh Manual Up in Mach3. I don't think they were ever implimented.
Could be wrong but I just tried it again with
5161 ----> G28 X value
5181 -----> G30 X value
5222 -----> G54 X offset value
They always come up as ZERO (0) not matter what it was set to.
Note : EVEN if they worked what good would they be without conditional Gcode

? That MIGHT be why they do not work, for me at least.
Just a thought, (;-) TP