My 2017 Band in a Box seems to have a problem saving instrument changes in midi files.

When I enter Sequencer to change the melody instrument, I select "custom" and then click OK but the file reverts to the original instrument and saves it.

Have tried F6 and the midi save icon but both no good.

Strayguitars

Sounds like the instrument patches are hard coded into those (presumably) imported MIDI files.

Since imported MIDI files all come into the Melody track, I would suggest going to notation view and clicking the "#" symbol to bring up the MIDI event list for the melody track. You will probably find the hard coded patch settings in the event list. Just delete them, then set the instruments from the main BIAB interface, and save.

What jford said. But, I do this in RealBand first then bring it into BIAB.
Look for lines that says PC or Program Change. Just delete them. Or simply change the PC number to the midi instrument number you choose. You may need to get the number from your synths manual though.