or just check if there will be a control voltage on the relay pads when You will try to run the probe. If it will be there You will jist need to solder relay in there.
Do you have any auxiliary relays on your IO board?
The macros you'll have to change are O09832, O09833, O09855, O09856
The stock macros work like this.
#1133 = Probe selection(Power is connected to relay center)
#1134 = Probe power(Sends power to relay #1133)
To use M relays codes you'll have to change these to the correct output. See Discrete outputs in the HAAS Operators manual
On my machine, I used the two extra relays on the bottom, for me #1118 and #1119. I put power to both relays rather than the haas way, and I simply turn on the one I want.
You can change your macro programs just like these other gentlemen have suggested or buy another I/O board. Also Haas offers a secondary m-code board if you need it.