I checked two different airline's FCOM as well as manufacturer's FCOM and they are silent on changing AB selection during roll out. AB definitely reduces the brake wear as it is a single application also it is even braking. Now the question of setting change, if company forbids then you must not but it remains company specific. System wise there is no problem. The objections that are valid are PF shouldn't do it, also even if PM did it it's a push button and may not engage so he has to ensure that it does and that cannot be monitored by PF who should be looking ahead. Besides selecting a higher rate is opting for more braking whether it will suffice is a guesswork. So taking over manually is a single action solution. However if someone wants to change AB selection during rollout it is not forbidden by every airline.