You can just swap them over. Before yoy start, remove the pads and pump the pistons out against the rotors. Then swap the hoses over, then lever the pistons back in to the calipers then you wont have to bleed them.
I would give them a bleed anyway, it’ll only take minutes, it’s inevitable some air will get into the system and you don’t want to find this out when your lever pulls to the bars on a fast descent. IMO obviously