My suggestion is to reassign the function of the mic button on keyboard from mic on and off to voicetron on and off and as suggested replace solid button with a button with an led.
Unfortunately, the current Ketron OS does not have panel button reassignment function.
On the SD9/SD90, "Vocal" is provided as the second fader from the right side of the panel for the output volume of vocal harmonizer. When both microphone and Voicetron are both On, moving the Vocal fader effectively achieves instant Voicetron On/Off and in-between vocal volume.
Thanks,
Paul