Originally Posted by UGBSM

Its not a matter of prerogative. Just because you are the Captain does not mean you can do anything you want without regard to regulation or policy. If you are going to violate the clear FOM jumpseat priority list then you better have a good reason and be willing to justify your decision to your chief pilot or supervisor.

So you would really love to say this to your boss? "I denied a Delta pilot the cockpit jumpseat in favor of an offline pilot because he wouldn't take the FA jumpseat".

Willful disregard of Delta policy can result in disciplinary action or termination. Look that up.