You can use the 'Update Engine Field' event to change any of the Platformer+ settings on the fly. The extra jumps one is a little tricky because the jumps reset once you land. So if you change the number mid-air, it won't update until you touch the ground again. You can also use the 'Update Platformer+ Field' to change the current number of extra jumps to increase or reduce the number before the ground reset.