So I have a cheap fender mustang 1 20 watt modeling ampand I am pleased with the way it sounds but I would like for it to switch from one setting to another when I turn my big muff on is it possible to trigger it to change settings when the muff is turned on
Epiphone Sheraton 2
Takamine Jasmine J33?
60's J bass copy (trying to sell or trade)
fender mustang 1
Victoria Regal II
big muff
seed of life overdrive

"We make music for hipster strippers" Dan Auerbach
you want it to change channels i asume. If so, the easy way is to get the switch pedal and place the big muff and the switch pedal close so you can switch with one step. Other wise it means heavy electronic thing

not without meddling.
punk isn't dead, it's always smelled that way.

"A perfection of means, and confusion of aims, seems to be our main problem."
^ extensively from what I've seen of the guts of the Mustang.

As marianoarnaiz said, place the Fender's footswitch next to your Big Muff and see if your feet are big enough to bridge the gap.
It's an opinion. It's subjective. And I'm right, anyway.