I hacked a CAMM-3, not hugely difficult because I had the circuit diagram and I was able to disassemble the Z80 code in the EPROM's.

Other people simply hacked into the stepper drivers and wired in MACH-3 losing access to all the pretty little bells and whistles.

The stepper software broke the motion down in to a series of straight lines and it was really neat. I ripped it off shamelessly. When you add accelerations and decelerations the following lines can affect what you do in the current line. Their trick made that easy. I had great fun writing an emergency Pause Restart but I become boring.

If you are not a total geek Mach-3 is the way to go