It’s perfectly possible, but the resources and ability to make that possibility come true is a different problem.
There’s no question that Dean’s smart enough to learn robotics, but there’s a reason he got a GED and never graduated. Hunting takes up most of his life and though he isn’t as obsessed as John is, he wouldn’t have the time to dedicate to learning robotics. There is a lot he would have to learn to be able to apply it. Then there’s the issue of getting access to the materials that are needed.
It would probably be faster just searching for a spell to shrink down a car to experiment with.