Can a laparoscopic gallbladder surgery site reopen 3-4 weeks post-op?

NO. It does not reopen after 3 to 4 wks later.
Which do you mean? It would be very unlikely for a laparoscopic skin wound to re-open 3-4 weeks after surgery. It would uncommon but possible for the fascia to come open late after surgery resulting in a small hernia formation.