Unless anyone finds problems, I've finished the work I plan to do on an alternate version of the Mac OS 9 app for macOS - a new version that keeps the disk images in the user's Library folder so that you can update the app without exporting and importing your disk images. Same download link as in the post two posts above this one.
I've added an option that copies the disk images back into the app so that you can then take the app to aother system. If you've created an additional disk or a user-specific disk, you'll have to back them up and then copy them separately to the new system. I've started building a framework for copying them into the app, but it's probably not worth the effort to complete it.
If this version interests you, please let me know of any problems with it. I'm not sure I want to replace the original self-contained version with this one, and it might make sense to make both available.