Thanks Dave,
The print options has a check box for triplet resolution which will SHOW the song either as straight or swing. It doesn't change the underlying melody however.
I found this and tried it. It is interesting but the lead sheets need to stay the same.
You can also try Quantize.
Select Melody | Edit Melody Track | Quantize, Time Adjust | Humanize Melody from the tool bar. There is an option to change the feel from swing to even. This does (I think) change the underlying melody, so it might do what you want.
But I don't think it will satisfy your request to "switch back and forth " but you could certainly save an even and a swing version and just pick the one you need
I tried all 3 Humanize options. You were correct. It chooses one or the other and does not switch back and forth.
I think to switch back and forth would be a lot of programming which is why I was thinking it is not available as a feature.
What is interesting is MuseScore can switch between playing straight 1/8ths and triplets properly on a bar by bar basis. However it does not have swing feel interpretation of 1/8th notes as far as I know. Ideally any such feature in BIAB needs to be set up with the ability to do these things.
1/ Set the individual beat subdivisions to match the style used for the current bar (a batch update).
2/ Tweak the individual beats to have either triplet or 1/16th subdivisions so triplets can be inserted in a Latin style or any combo possible such as inserting 1/16ths in a swing feel or even double time (division of 6 per beat).
For our jam group it would be a very low priority request. Not sure if there is much money to be made from such a programming effort.