Mike, after editing the MIDI notes or voicings into the ones I want, do I just immediately freeze the arrangement, or is there a missing step or two there (like save first)?

Noel, you would never want to play the full "stacked donuts" chord on a 13th unless you raise the 4th to get a 13#11, because the fourth is an avoid note that destabilizes the desired sound. Bbmaj7/C is actually a 13sus, not 13.