Exchange cars with each other – Questions for re-registration

Moin, in advance: I will still ask at the registration office, but wanted to get some opinions and suggestions here in advance, because here some are represented with good knowledge. My father and I want to exchange the cars with each other, say he takes over mine, I his. Now the question arises, how to do this with the re-registration best, because there are from my point of view points, which could become a bit tricky: We live in different federal states and want also In addition, the letter of my vehicle is still with the bank or with the dealer. The vehicles are probably exchanged with me. My father also depends on a seamless re-registration on himself, if his car (which is then mine) is registered with me for a few days, that would be no problem. I have the following thoughts: 1) Ideal solution. We meet with me, drive together to the registration office and everyone reports the different vehicle to each other. I would have my car’s letter sent to the registration office before. I have considerable doubts, however, that in Lower Saxony a car can be re-registered to my father who lives in Dortmund. Am I right? Then this would fail. 2) My father registers his car in Dortmund and at the same time applies for a short-term registration mark. He then comes to me in Lower Saxony by car, we exchange the cars. He drives my car to Dortmund, reports it to himself. (I would then send a letter to DO) and send me the number plates. Here is my question, if I can then register his old car on my number plates, or if then a blocking period enters? Is there still a possibility, which I have not considered to date? And which ideally can be done without the additional item “short-term identification”? For example, the financing is all so far clear, borrowers and holders do not have to be identical, the car can change at any time any and the letter will be sent accordingly to the corresponding registration office.