Thank you, karl - that is an excellent troubleshooting technique, wish I’d thought of that myself (“doh!”).
In the meantime, for benefit of anyone else later who might have the same problem: someone (“Bad Mister” - godlike status dude!) in the Motif forum pointed out a way to do this from the “List Editor”, and that works like a charm. As far as I can tell, “Program Change” is not an automatable parameter, so it has to be done another way … as in editing the “List Editor”.