There are two ways to get the motor disconnected from the wiper system.
#1. Pry the socket and long rod off of the ball that is on the short arm. This may be a bit difficult, but is the way that the long rod was assembled onto the ball. This method also maintains the spline clocking to the gearbox output shaft. If you are moving the short arm over to a new motor, you have to reset the wiper motor clocking (power it up and sweeping it once) before installing the short arm in exactly the right spot on the splines.
#2. Remove the nut and pull the short arm off the gearbox output shaft. The shaft is splined and tapered. This may be somewhat easier than method #1, but risks wiper system mis-clocking. Realignment to correct clocking is not difficult, but requires reset of the wiper motor clocking (powering it up and sweeping it once) and then making sure the wipers are in exactly the right (resting) position before reconnecting.
For changing the electronics module on the bottom of the motor, my preference is for #1......
I would encourage anyone... everyone... who asks how to do something and discovers a solution, to bring the thread full circle by sharing what happened. Otherwise, anyone searching the archives for the same question ends up with a dead end.