No, you'd be wrong about that. State vehicle registration law does not override federal trademark law. As soon as you are damaging the value of their mark, you're history.
Not exactly. Factual use of a trademark by a third party is not infringement. As long as what you are selling is an actual Ford product, you are free to call it a Ford without Ford's permission, and they cannot stop you. If your company customizes or modifies a product and resells it, you can call it what it is by using the original manufacturer's name and product name. You cannot imply that you are that original company though. See, for example, Lingenfelter's marketing of Chevrolet-compatible parts and customization of Chevrolet vehicles. Similarly, you can use a third party's trademark to factually identify what your product works with. For example, an independent company that makes iPhone cases can call them iPhone cases and identify which models they work with. They cannot label their own product an iPhone though, or imply that it is made by Apple.