Can you paint a car with out sanding it?

If you want to have a nice looking finish that will last mare than a day, then you really need to sand it.

If the existing paint job on the car is perfect already, and all you want to do is change the colour, I'd use some 800 then 1000 grit paper very lightly. Be sure that ALL dust is removed (alcohol works well) before painting.

Paint in a dust free environment

Use resiprator and paint suit.