There is another method to delete and replace that MIDI track.
1-erase the MIDI track
2-freeze that track - you will be asked if you want to regenerate that track-say no
3-while frozen regenerate (may not be necessary but I do it to make sure the MIDI track is erased
4-while frozen pick a new MIDI/RT instrument if you want
5-while frozen regenerate (may not be necessary but I do it to make sure the MIDI track does not reset to the original voice- I know I'm paranoid.
6-unfreeze track
7-regenerate and the new sound will be there.

If you only want to erase the track stop at #3.

I want my last spoken words to be "I hid a million dollars under the........................"

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware