Definitely. I witnessed a flight that was almost pulling onto the runway to depart, turn around and come back to the gate because Dispatch demanded a few crew-members who needed to deadhead out needed seats, so lo and behold I got to go on and order 2 standby pax off that I had cleared bc dispatch decided (about 10 min late) they needed to send that crew back.

Although doors should never be re-opened for ppl to get on that missed in my personal opinion.