A couple of things to try

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.

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


BIAB for Windows Version 2019 (643)
Windows 10 (1909)