Well, I'm not using MacOS anymore. I switched to Windows after I got fed up with Apple's increasingly shitty hardware and repair services. I'm gonna have to learn a Windows-based music composition program, then bring up my old music on one of the old Mac computers I was working on, and copy it to the new program using the ten-finger interface, 'cause I don't know of any other way to convert musical scores from one proprietary format to another.

Then again, it may be using an open format. I'll have to do some research on the .myr and .mus extensions (I imagine there are several file formats with those extensions so it may be kinda difficult to pinpoint the right one), because those are the extensions that Melody Assistant uses/used.