Under normal circumstances, you can only use one frequent flyer program at the same time. It's either Flying Blue, or Skymiles, but not the status perks from one, and crediting to the other, even though this is technically possible (see below).

If you want to use your status perks, simply change (or call and ask the agent to change) the frequent flyer number on your reservation to the Flying Blue number. No need to "rebook", the number can simply be changed. You can do that yourserlf in My Delta or have an agent do that at any time. Keep in mind: this removes the Skymiles number and the reservation will disappear from My Delta when logged on to your SkyMiles account. You can still access the reservation the old fashioned way though, by entering name and PNR#.

If you attach your FB number to the reservation, your status will automagically be applied. You will earn miles and XP on your Flying Blue account for that flight. If you really want to credit the flight to Skymiles, but use your Flying Blue credentials for status perks, you could /try/ to have the gate agent change your frequent flyer number back to Skymiles, just prior to boarding. Just tell them you noticed that the wrong FF flyer number was attached and you really want to credit this flight to SkyMiles. No guarantees, but they usually will change it for you..At that point, your preferred seat has been selected, your extra bag is already checked and your boarding pass has SkyPriority printed on it.

Technically, at least on the KL side of things, this is possible though. The PNR contains seperate fields to store frequent flyer numbers for earning and status purposes. FQTV is for earning and FQTS is for status recognition. I don't know whether that's also the case on the DL side of things though. But common practice is that both should be the same and you don't have access to these seperate fields yourself.