IFF- good question. Had just this on take-off roll on a 747 at Orlando. After setting thrust and before Throttle Hold, we were concerned at the wall of weather ahead and local reports of windshear, so I hit the TOGA button again and got full power (it was lovely, 4 RB211s going up to full chat- glorious sound, and a noticeable surge on roll in a moderately heavy 747). I'm not sure whether it would still work after Throttle Hold, I think maybe not though as the Boeing 737 Flight Crew Ops Manual (11.32.3) states "if conditions are encountered where more thrust is required, the crew can manually aply full thrust." Remember, you are in Throttle Hold so you can do what you like with the throttles, and the automatics will take no further interest until ARM mode at 400'RA and 18 seconds from lift off (oh Heavens, I must get out more!)
PS I finished a 737 tech course yesterday (that's my excuse).