hey Leon
in a T3 you can't set an expression pedal globally you would have to do it for each program and combination separately ,unlike the M1 it was done globally which was better because in the T3 case and i think it was a big stupid mistake made by korg,the fact that you have to assign each program and combination to work with the exp.pedal caused on major problem that is every time you change to a different prog/comb. the volume comes to it's maximum and to prevent from scaring the audience you would have to press your pedal down and up again.
i hope i explained it good enough and didn't confuse you ,let me know if you need further help.
eddy