It's well documented that bounty questions whose bounty period expires without an accepted answer have some delay in auto-accepting an answer (here and here). Is it possible for the OP to accept an answer on an expired bounty question after the bounty period expires and before the auto-accept job runs? If so, can the user accept any answer or only the one that would have been selected by the auto-accept feature?
I'm pretty sure I've had full rep (i.e. not the half-rep for auto-selection) from a bounty question after it formally expired, with a comment from the OP at the same time, so yes, in theory this is (or at some point: was) possible.