I do this all the time. Modify a copy of the maxinterface.json file (be sure to keep a copy of the original). Then, after you build your standalone, replace the maxinterface.json file that is automatically included in your app’s Support>interfaces directory with the one you modified.
If it is impossible, I’ll settle for that. Anyone know? I remember reading in an old thread here someone stating that using maxinterface.json you could do away with the [menubar] object completely, but no further explanation.