Window Motor Replacement

My 1991 Mercury Grand Marquis needs to have the driver's window motor replaced. The shop manual states "WARNING: PRIOR TO MOTOR ASSEMBLY REMOVAL, MAKE CERTAIN THAT THE REGULATOR ARM IS IN A FIXED POSITION TO
As this was written in all caps (in the manual), it must be very important to do so. Any ideas on how to do this? My thought was to run duct tape over the top of the door frame and then down both sides of the window (in 2 places).
Any help would be appeciated.
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