The thrust is scheduled by the Autothrottle/ Thrust mode logic.
When you push the TO/GA buttons, the Autothrottle engages in ‘GA’ mode, in this mode, the first push of the buttons gives reduced go around thrust to achieve 1000-2000fpm. The second push gives full go around thrust.
Engaging level change during a climb, causes the Autothrottle mode to change to ‘N1’. The N1 mode is programmed to schedule CLB thrust.