Can the active g code program be changed via the PLC?

[cncsnw]

You might still want to do something like the computed M98 two posts up, but without the GOTO loop. That way you don't have to change the loaded job (which could introduce timing challenges); you can just have the dispatcher program that is always loaded call up whatever numbered CNC program file the input bits identify.

You can indeed have numbered program files from O0000.cnc to O9999.cnc, though it would probably be best to stop at O9099.cnc for typical use. Centroid has some special treatment for program numbers from O9100 through O9999, which, while it does not preclude using those numbers for freestanding programs, encourages use of those numbers for subprograms that are embedded within other programs.

To identify any possible program number from 0 to 9099 (or 9999), you would need 14 bits of inputs from the robot to the PLC, or would need to devise some sort of home-grown serial protocol.