The tyros has an execute setup functionality in the second page that let's you save the settings you set in the mixing console if it settings you do after you have recorded the song, if you reset the song without executing the setup you lose the settings you made. If you want to change the levels in real time you need to record them and then execute the setup, or you should be ale to do it in the evvent edit.

BTW, the song editor in the Yamaha Tyros really sucks. Try something like a Korg Trinity (or a computer) and you will notice this.