@Paul Ennnn that's rather easy to remove. It's similar to play-doh when you play with it (at least the one I own), little harder but remains fluid, meaning it's not keeping the form. It's a non-newtonian fluid. It would cover fragment of the car, at least in places where paint is thin (i.e. no putty to fix dents, no multiple paint layers covering deep scratches), but it's very easy to remove. It's easier to remove from metal plate than from a carpet In fact, there are more substances like this, check out for ferro-fluids. They behave little differently, because while putty is magnetic, the fluid is not, it's metal, it needs a magnet to reveal its true form.
I'm not sure how this putty is made, but for ferro-fluids you need ferromagnetic dust - a compund of oxydized iron, and oil. I imagine that for putty you need to have, besides silicone and soap, strong magnetic dust, like from rare earth magnets.
The magnetic putty is rather weak. I can compare it to common fridge magnets.