For the B3 you can always go into "mixing" and/or performance screen and touch "mute" for that part for a temporary disabling or delete it. Touch the part and a menu will appear to "search" for a replacement part or delete it completely. If you're not sure which part it is you can press "solo" for each part to determine which it is.
As for the assignable buttons I haven't tried that yet but there's a controller option for those buttons. I'll see what I can find.
It appears that you need to press [Edit] once you select the part for amp distortion and then look for "Mod/Control" and then "Control Assign" on the edit page. See photo for a similar page. Then you'll see a box "Source" and once you select that a big menu appears for assigning anything to a controller. You will see Switch 2 after you expand the menu. Next look for the 4 "Destination blocks" where you can chose from insert effects "A" and "B" and whatever effect you need. I'd play around and see what changing those accomplishes. See next post.
Here are some related screen shots. It looks like you have to select a parameter of the insert "A" or "B". You'd have to know which parameter you need to assign. I just tested this and it did work. I assigned InsA dry/wet to switch 2 and upon pressing that switch the effect changes. In the "effects" section is where you'd select amp distortion for your performance. One nifty trick is that while the menu is open for selecting a controller you can leave the switch 2 active and tap on each of the many options and the tone will change accordingly in real time. Nice! I found tonal changes that I never would have designed for just from auditioning the many options under "Element" for example.
I've got a B3 part in a performance that I'd like to turn off and on the amp distortion effect with the Assign 2 button. Anyone know how that's done?
Brady, the question is too general to give you a specific answer, but in general, a Distortion assigned to an organ sound is typical an Insert Effect, any Insertion Effect has several real time controllable parameters. Most of the Preset B3s that use distortion already have a CONTROL ASSIGNMENT that allows you control it. In each case the Super Knob either brings in the Distortion or removes the Distortion by adjusting the "DistortionDrive" setting.
Find it and switch the SOURCE to the Controller you prefer. You will most likely need to scale the amount to suit your needs. While the Super Knob (controllable via an FC7 pedal plugged into the Foot Controller 2 jack) either increases or decrease the amount in a rather smooth fashion, the ASSIGN SWITCH will be either On or Off, so you will need to scale the amount using the Ratio parameter.
There are so many different "Distortion" algorithms - some will allow to adjust the "Overdrive" amount, some have a "Dry/Wet Balance", others a multi position "Distortion Switch"... Perhaps if you tell us which Organ Preset you are working with we can point you in the right direction.