I bet it would work good for that. Since the pattern, say racing numbers or something on the side of a car, would be small in size to get a nice even application even out of the can.
THE ONLY THING. would be the masking. Since the shit would stick to the tape, just as good as the car then you go to peel the masking tape/pin stripe tape&masking tape for your design, i wonder if it will lift the plastidip off the painted surface too? Kind of like when you paint a car with graphics and did a shitty job scuffing the surface, when you go to remove the masking it lifts the paint and fucks up the graphic.
The thicker the application the more the chance you have of lifting the graphics when you peel the tape. What we usually do is carefully take a razor blade and ever so gently cut the edge, between the masking and the painted graphic you are leaving behind. On a permanent graphic this is perfectly OK, since its getting cleared and the slight cut will never be seen. HOWEVER if you do this with that dip stuff and go to peel the design off later on, you might see a razor blade outline in your paint!
I would say make the plastidip graphic as thin as possible application thickness wise to cover evenly. wait forever for it to dry 110%, then pull the tape carefully and off the car parallel against the surface, not 90 degrees to the surface. This will make the masking more or less roll and cut as its removed, instead of yanking off the surface. its hard to explain the technique in text.