No, this is not possible.

To begin to understand why, you must consider that to change Transmit Channels of the Keyboard, you do so by selecting the Track of the Sequencer. You transmit from the Keyboard via a Track of the Sequencer to the Tone Generator.

The synth does not really address itself with MIDI. It can generate MIDI messages for external use (documentation to a Sequencer or controlling external devices).

On your MOXF:
The MIDI Channel is determined by the Track. On your MOXF, when the

button is lit, the buttons 1-16 select the MIDI Channel on which the MOXF Transmits. This is true in Voice, Performance, Song and Pattern modes.

A Foot Switch cannot change the Track. To change the Track (and therefore the MIDI Channel you are transmitting on) you must press the Track button. The Foot Switch can be assigned to certain messages: cc numbers are Channel Control Change messages. Yamaha has selected certain of these to address specific global functions: Master Arp On/Off, Sequencer Start/Stop, Program Change Increment, Program Change Decrement, and Octave Transpose Reset.

The Program Change Inc/Dec will change the Current Voice, Performance, or Song/Pattern (the entire Mixing + Seq).

The FS cannot be used to change Transmit Channels, sorry. The buttons are there for this purpose.

The Sustain pedal (your other, dedicated, Foot Switch) can be used to hold the sound(s) assigned to Channel 1 while you press a Track button for another Channel and begin to play the sound(s) assigned to the new Channel. This allows for smooth transitions between the sounds you’re playing — but you do have to press the button.