Before you use acetone on metalic paint do a test somewhere out of sight,…..under the wing of under a scuttle etc., to be certain that the acetone does NOT go for either the paint sirface or any laqueur that has be put over the top.
Depends where it is & how big but perhaps he could source a little lable or rondle etc something like that. Ie a security tag ( if near the lock) etc & put it over it so it looks as it is supposed to be there
Superglue shouldn't set if it has free access to air, so should be able to wash off with warm soapy water. The edge of a credit card or similar can be used as a scraper which shouldn't scratch the paint.
Nitro Methane is the most effective solvent for super glues. It usually does not effect the car paint either. Acetone can attack some car paints. Some superglue de bonders contain Nitromethane.