EV5 pedal to control volume

[bibiche]

hello everyone,
I just bought the EV5 expression pedal to control the volume.

I have 2 questions:
1/when assigning the effect in menu/system/pedal/ control pedal: what is the difference between the expression and volume category?

2/when assigning my pedal to volume, it seems impossible to control manually the volume anymore.
I prefer to be able to control the volume both manually and the pedal (only when my 2 hands are occupied).
Is there a way to do that?

thank you very much for your help!