I guess Ryanair has carbon brakes fitted in most if not all their -800s?
No they don't.
Boeing SOP would recommend setting the brake as part of the RTO before getting around to assessing the problem causing the RTO. The alternative would be for you to stand on the brakes whilst making an evacuation decision, setting it then if not forgetting it (much more dangerous).
But, once the decision NOT to evacuate is taken, when taxied clear of the active runway, return to the cooling schedule guidelines and follow them, eg consider not setting your brakes.