I wonder if the good folks at Garritan have considered providing a MIDI control channel that would support the same functionality as keyswitching? While keyswitching instruments are fine when playing from the Kontact Player, when using GPO in a sequencer, adding keyswitching notes has an important downside. If you transpose a MIDI region, the keyswitching notes are also transposed and the instrument effects are messed up. This becomes a problem when using sequencing software like GarageBand and Logic, which supports the transposition of regions without even looking at the midi note data.
I have read through the reference manual for both the Kontact and Kontact 2 versions of the GPO library and have not found such a CC. If I have missed it, my apologies and I only ask that someone points me in the right direction.
Otherwise, the provision of such a CC would seem fairly straightforward. For example, suppose CC 24 was provided for this kind of control. CC24 = 0 could mean use the keyswitching data embedded in the midi data (i.e., operate as now). CC24 != 0 could mean use the CC24 value for keyswitching and ignore notes in the midi data outside the range of the instrument. CC24 =1 could specify the same behavior as the lowest keyswitching key for the instrument; CC24 = 2 could specify the same behavior as the next keyswitching key, etc.
I realize GPO has just gone through a major upgrade, moving from Kontact to Kontact 2, so perhaps this is an unwelcomed suggestion. However, I do believe it would improve the usability of GPO in at least GarageBand and Logic. (correction to original message: adding CC "keyswitching" support would not be useful in Garageband, since GarageBand does not provide access to MIDI control channels. However, it would be useful in Logic, Logic Express and perhaps other sequencer software).