Devalue the license plates themselves and then go to the registration office?

Hello, the following problem. I’m going to sell my car tomorrow, buyers were here today and did a test drive. But since the application for a short-term license plate takes 3 weeks, I wanted to go with the car where the car is parked, the license plates are devalued and so be sure that they can no longer drive with it. The devalued license plate can be taken to the registration office afterwards.