While you cannot re-assign the expression pedal in that way, there almost always is as way to have the XPDL serve the different functions as desired - for example, by having it controlling different parameters in different scenes or even within scenes by changing bypass states and/or channels of FX blocks. For example, I have the same XPDL sometimes control wah and sometimes control volume and sometimes specific FX parameters (like delay time or feedback, or pitch mod in the pitch block ...) without having to reassign anything - i.e., and pressing either a control switch or changing scenes results in the XPDL controlling the different parameter(s).
If you give us a specific preset or scenario perhaps we can provide insight on how we might address it - in the 'wah' vs 'delay mix/feedback' scenario, for example, as alluded to above you can have the XPDL controlling wah in one or more scenes, but then in the other scenes the XPDL controls the delay mix/feedback - either by assigning the modifier only to one scene or by using the mixer to, for example, bypass the wah in the scenes where you want the XPDL to control the delay mix/feedback (i.e., the XPDL is still assigned to and controlling the wah, including the auto engage feature, but because the audio from the wah is muted by the mixer it is effectively 'bypassed').
