[LAU] Usage of undefinded MIDI mesages

Hi, I have turned an old analogue electric organ into a MIDI controller. All the old push buttons, switches, pots, drawbars can now trigger MIDI events. Because I would like to make the MIDI messages static (i.e. they are linked with particular buttons and faders and will not be changed) I have thought of using an external application (keykit in this case) to work on incoming MIDI events of the MIDI controller, filter them and trigger newly defined MIDI events with it. I would like to make the MIDI messages transmitted by the controller as short as possible. I have thought of assigning the Bx (Control Change) command to the buttons and faders, but this would mix with/overwrite other control change commands sent by other MIDI devices. It has to be possible to distinguish between the buttons/faders by the MIDI message that each one triggers. How about the System Common Message F4 and F5 which are not yet defined in the MIDI standard? Could I add some extra data bytes to identify the type (button or fader), the number and value? Like this: F4 125 70 (Fader 125 sends value 70) keykit would recognize this fader and set volume level for channel 2 for fluidsynth. Or, in another situation, increase sustain value for channel 3 for fluidsynth. or: F5 10 1 (Button 10 sends value ON) keykit would recognize the button and turn on sustain for channel 1. Thanks for any hint and kind regards, Crypto.