OK guys, thanks for the info. I read the manual and it seems you are correct. However, it states the clutch should be pushed to start the tractor but it starts just fine without pressing the clutch pedal. The manual also says to start the tractor in the neutral position of the range select. This also is not a requirement. I suspect these are "for your safety" but not requirements. Only having the PTO engaged will prevent a startup.
While not moving, I have changed between 2WD and 4WD several times without issues. I also think you can change ranges when not moving without the clutch. My old Simplicity legacy had no clutch, but had a high / low range hydrostatic. Mine was 2WD, but some were 4WD. In either case, the range or 4WD change had to be made while not moving but there was no clutch. "Hydrostatic neutral" makes sure nothing is spinning.
By the way, how is 4WD engaged? As in, what is physically happening when you pull the lever?