Which of the following actions is considered unlawful alteration of registration plates?

The action that is considered unlawful alteration of registration plates is mutilating or covering part of a registration plate. This is because such actions can easily obscure important information, such as the registration number or other identifying features, making it difficult for law enforcement to identify the vehicle. The integrity of the registration plate is crucial for vehicle identification and enforcement of vehicle laws. Mutilation or covering may lead to instances where a vehicle may be unidentifiable, potentially aiding in criminal activity or evasion of law enforcement.

In contrast, while certain other actions might raise regulatory issues, they do not necessarily constitute direct alteration in the way that obscuring or damaging the plate does. For example, replacing worn-out numbers or repainting a plate in a different color can sometimes fall within legal provisions if done in accordance with state law, and transferring plates between vehicles, while regulated, does not change the physical integrity of the registration plate itself. Therefore, mutilating or covering part of a registration plate represents a clear violation of the law intended to maintain transparency and accountability in vehicle registration.