How to reverse the sustain pedal in MainStage
Step 1: Open your MainStage concert, and go to concert level by clicking the name of the concert at the top of the patch list
Step 2: Click on the on-screen sustain pedal
Step 3: Make sure that it is mapped. The assignment should be: Send to All > (your keyboard name here) > 64
Step 4: In the Mappings tab, change the Range Mode to Inverted.