One of my many jobs at WDW was in the parking lot...and yes you are definately allowed to be 'not as magical' as other CMs.
There are safety issues that come into play and frankly a lot of guests don't want to follow the rules. There is a specific way to park cars that helps minimize traffic back ups onto the feeder roads...this is crucial at peak times. One car doing it's own thing screws it up. They want to get cars parked fast. They want people to walk in certain areas so they aren't hit.
They don't want people jumping on and off trams.
I promise you, every parking lot CM has a stoy of some guest falling off their tram. They've all been hit by cars...screamed at, sweared at...SPIT at. Told off for trying to make someone go down to the end of a row.
Trams are 15 ton vehicles that can NOT stop on a dime. Each car has a seperate air braking system so it doesn't jacknife. There is no reverse.
Lot CMs are a great group, if you follow the rules. However, their formost job is to keep guests safe. While they try to do that as nicely as possible a lot of times people don't respond to nice suggestions.