However the STOP actions will require the throttles being closed and then placed in the idle reverse position. This will ready the engine for a reverse power application if needed.
I don't know about a 777 but a stop decision at high speed normally would assume full reverse especially on a wet runway where braking efficiency is less than on a dry surface.
If the cause of the abort was an engine fire warning, consideration should be made to not use reverse on that engine to minimise chances of the reverse plume spreading any fire to the fuselage. See report on the British Air Tours Boeing 737 disaster at Manchester, England in August 1985. In that accident the fire erupted from a severe fuel leak in the left wing caused by red hot shrapnel from an uncontained engine break up piercing the underside of the wing tank. The reverse thrust plume atomised the fuel causing a huge fire that breached the fuselage.
http://www.skybrary.aero/bookshelf/books/374.pdf
Also, the act of selecting idle reverse during an abort means the reverse is at ground idle instead of flight idle. In the 737 for example, flight idle drops to ground idle four seconds after touch down. That means a longer spin up time to get full reverse.
If the pilot decides brakes only deceleration is too slow for his liking, by the time he realise it and selects full reverse, it takes a relatively long time to wind up from ground idle reverse to full reverse. By then the speed is probably quite low where reverse is inefficient anyway.