I don't think you can use KLM miles to "pay" for an upgrade and then credit the flight to DL. Moreover, if there were earlier flights on the ticket/PNR that you credited to KLM, you should note that DL won't permit you to change the FF number on an itinerary after the first flight has been boarded/flown (or maybe even the cutoff is when you check in?). DL apparently won't permit you to use one FF number for status benefits and a different program's FF number to credit the flight. [Some carriers such as SQ and others in *A are known to permit this and in fact have two FF number fields in their systems.] On the KLM side, once you use KLM miles for the upgrade, the system probably won't permit you to credit the flight to a different program or to change the FF number on the reservation.