Applying more brakes early will force the brakes to absorb more energy, therefore increasing the chance of overheating. Remember that Boeing Autobrakes (other than at Max or RTO) attempt to maintain a constant deceleration rate, not a constant energy-absorption rate. Because energy absorbed is proportional to the square of the ground speed, the brakes can withstand a higher deceleration rate at low airspeed without overheating. Clearly, using max Reverse immediately after touchdown will help prevent brake overheating by dissipating much of the energy that would otherwise be absorbed by the brakes.
AFAIK, OPS only 'worries' about the Maximum Brake Energy published by Boeing, and NOT whether or not the thermal plugs might melt. Also, OPS (as configured for our Classics) did not use Thrust Reverser credit for the Operational Landing Performance.
Note that the limit certification criteria for a rejected takeoff only require that a severe fire will not break out for 5 minutes after a max-TOGW rejected takeoff. Thermal plugs merely help prevent tires from exploding when they are overheated, so they may melt well before the max brake energy is absorbed if a tire is heated quickly by hard braking at high speed.