Thank you

Hello, I hope someone sees this and can help me. I have been given the task of adding 2 new M-Codes to some of our machines. CNC machines aren't my strong suite. I generally program PLC's and robots. Mazak shows several M-Codes that aren't assigned a function. We would like to use M66 and M67. I have looked through the PLC program of a machine that someone started this process on and I can see the M66 and M67 used in several locations. If M66 and M67 are located in the correct locations inside the PLC to perform the function we need will they work when called from the CNC controller or do they need to be enabled somehow?