When you change your shifter to run a left hand prop, is there additional adjustment to be done? Or, do you just attach the cable to the other side of the lever and roll? BTW, I have Merc zero effort controls.

"just attach the cable to the other side of the lever and roll?"
That's all I had to do. Getting it hooked the first time was a little tricky, but it gets easier with every change.

Just switch it at the lower end of the shifter Dave.

However, there is a special Mercury calibration tool for fine tuning the shift linkage on top of the motor. You probably don't have any reason to need this though.