Yes, the constant trick question is whether it is load-bearing or not and if those boxes contain any load-bearing beams or joists.. it's not entirely easy to see when it's all painted, trimmed, and finished..
One way might be to check if any building permit has been applied for the change. In the best case, there might be some drawings and calculations at the municipality that reveal how it is done..
IF it is not load-bearing and possible to remove in its entirety without reinforcement, you would either have some trim left that hides the transition or you would have to install a new ceiling in those rooms to get the same ceiling surface or some solution to redesign those ceilings so they match each other.