Midi programmer needed for firmware modification vintage midi synthesizer

I'm looking for a programmer who can make a modification to the firmware of a vintage digital yamaha synthesizer. (TX816 built in 1985). The firmware is burned on an eprom. (I can get the code using an eprom reader) but I'm not even sure if the hex code can be translated into something usable. This is what needs to be done: The TX816 is a rackmount synthesizer. It is able to receive aftertouch data from a midi keyboard an use it to apply different effects. It only accepts "channel aftertouch" though. I would like to make it able to read "polyphonic aftertouch" messages so that the effect can be applied for each key individually just as it threatens velocity messages individually. The reason why polyphonic aftertouch was not present on the TX816 is most likely the limited midi bandwidth. But using a computer between my keyboard (with polyphonic aftertouch) and the TX816 I can lower the resolution for this specific data stream.