The key with the Vamp Pro
seems to be that you make your MIDI pedal turn off distortion and effects thru the change code operational mode. It is my understanding that its not the goal of the Vamp Pro/Vamp-2 to be able to switch patches as you would channels. Rather, you have a patch (like Plexi Marshall) that you can CC a distortion pedal
in/out, FX in/out, and any other MIDI controlled CC function (like a variable controlled pedal). This happens in real-time and mimicks how a real amp works (gain in/out, FX in/out).
What I do is have an amp model for a particular song and have CC codes hooked to a pedal to add gain, pedal, or pre-set effects (like chorus/flange/AutoWah). Thats as good as it gets.