[quotePost id=120800]But it still seems to me that all that is needed is a user 'flute' voice with a restricted note range using SysEx or an external tool.

Then when you load that user voice into slot 3 and select it it does what OP wanted to do.

Is there a way to have Part 3 flute replace only the right-hand organ part?

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The reason that won't work is that, when he selects part 3, yes, he will get the flute sound over just a restricted note range, but he will also simultaneously deactivate parts 1 and 2, which means he will lose the piano that he still wants playing over the other half of the keyboard. We need a way to activate the flute (over the desired keys) while ALSO keeping a piano sound on the other keys.