Hi,
you could try the freeware "PSRUTI", itīs usually written for Yamaha PSR-Keyboards, but (batch-) revoicing is very easy with it
.
I used it to revoice my Yamaha-Tyros1-files to GM ("GM-revoicing") and then the "midifile Optimizer" ( 150 ... ) to revoice it to Audya.
Youīll find it
HEREFor english language scroll down a bit