Line 6 M13 Stompbox Modeler - Order your mods for this unit here.
Yes, you can have two expression knob and two double preset mods on the same unit - BUT - you will only be able to have one or the other active at a time.
A toggle switch will be installed in situations where you are ordering more than two total expression mods.
IE; if you choose "Expression Knob (EXP JACK 1)" and "Double Preset (EXP JACK 1)" -- these will both be assigned to the 'pedal 1' option under controllers; BUT you will have to have a toggle to use one or the other -- not both at the same time.
If you want both and don't intend on switching back and forth, it'd be better to get "Expression Knob (EXP JACK 1)" and "Double Preset (EXP JACK 2)" so that each one can be assigned as each expression pedal.
Hopefully that makes sense.