Thank you guys.
What about this; the XSonic Airstep?
It’s a midi controller footswitch that can send midi via usb, Bluetooth and 5 pin.
On their website it says it can act as a USB Host when you use the USB port;
“USB HOST: USB HOST is a unique function of AIRSTEP. In this mode, AIRSTEP’s USB interface is equivalent to the USB on the computer. It means that you can plug-in devices that can be controlled by the computer. Many hardware effects only have a USB port, which is only controlled by a computer, like the ZOOM MS Series, now you can use AIRSTEP to extend more footswitches for them. You can also plug in your USB MIDI controller to AIRSTEP, it will power the controller directly, and forward MIDI messages to Bluetooth, then, your controller becomes wireless.”
Would I be right in thinking that if it can act as a usb host, then it should work to control the patch selection on the amp (which uses Program Change messages) just by plugging it in directly, and without any other hardware/software required?