I was facing a daunting task of putting a lot of the same parts in one gcode file. I took my time and did 60 control horns all grouped in order. The code could note be made. Have a few ideas why but that's not going to solve the problem.

A little searching in Mach found the nesting wizard. A simple row and column kind of thing that requires a slight mod to the original code via notepad. You change the M30 in the last line or so to a M99. I made a copy of the code and did the change and use that code for my nesting and the original for testing.

I gathered a tight compact grouping of what I needed repeated and used the wizard to multiply it up.
When running the wizard you change the number in the 'row' box to what you want and press 'enter'. Do the same with the column box. Make note of your new X-Y maxes. The viewing area shows the change but I haven't found a way to save the new code. Which looks like a subroutine call out script, but what do I know.

 

You should be able to hit the edit gcode button once you are back at the start page and then you can copy and pate it into a blank txt firl that you can just rename replacing the .txt with .cnc
Let me know if that works for you , I have not looked into this much (wizards) but it should work as long as you can exit from the wizard back to the cut page of mach3
Mark