Isn’t the Probe connection on that new riser board the same as the circled header? (I’ve got what is now a really old version of the controller) If so (pinout matches), that would eliminate the splitter.
P = Probe
F = Feedhold, in case you want to wire a feedhold button (see this)
The one on the right is an alternate for Probe, but I don’t know which of the three pins is which (5V/Probe/GND…easy to figure out if required)
So, from the link to the Feed Hold button thread, and if I understand it correctly, an intermittent switch connected to the outer two pins on right hand riser (as shown in the red rectangle), will initiate a Feed Hold on first press (which will raise the spindle and turn it off if a BitRunner is fitted) and a Resume on the second press?
Almost. A first press will initiate a feedhold (= have the same effect as using the “Pause” button in CM), a second press will do nothing at the machine level, but will let CM go back to a state where the “Start” button is enabled again, at which point you can press “Start” and it will resume the cut.