I'm thinking of removing the audio control button to replace that area with a A/F guage but will come up with another place if I cant use the mute for the audio control functions. I know the audio control just cycles through functions whereas the mute is on/off but perhaps its possible and maybe even easy to swap the functionality.

Has anyone tried this or seen both to know how feasible it would be?

 

not trivial, but it (like anything else) could be done.
the mute button sends a +12v signal when pushed, while the mode
button changes the resistance to ground when pushed.
one could create a circuit with a relay and a resister that mimicked
the mode button when pushed.
for an explanation of what the various buttons do, see:
http://www.modifry.com/products/dci/tech.htm

 

Actually, once the panel is removed, it should be relatively simple. Just move the switch contact wire from the audio control button to the mute button. Of course the led in the mute button would no longer function. The switches on that panel hook to a series of resistors. Those voltages are decoded by the radio. Aftermarket devices like Modify's DCI decode those voltage changes and output them to aftermarket head units in a format they understand (for example, the appropriate infrared pulse codes for a given head unit).

 

Now that I think about it, and reading oth's post, it may be more difficult than I thought. Those resistors may reside on the circuit board associated with that panel. Modifiable possibly but not necessarily simple.