In my opinion, Rhino needs a command that can open all hidden toolbars and highlight all icons that contain customized commands, i.e. everything that does not ship with Rhino by default. Running that command again should return the previous state of the toolbars. Sort of a Toolbar state manager, maybe?
Also, a command line option of this icon must let the user choose if the highlight of all non-default icons will remain permanent (like changing the background colour, adding an outline, or a tiny triangle or a plus symbol in the corner). It must be possible to remove the highlight at any time.
Since it’s copied or moved to a custom toolbar, it should be highlighted as well. Just like anything that’s not default.
The highlighting will help the user see which icons were modified, thus they could be checked for errors, for additional modification (or removal) or when the user forgets where he or she placed a certain icon.
I believe that this should be considered a non-default toolbar, too, despite the fact that it does not contain a new or a modified icon. It just lacks one default icon, but the remaining icons on the toolbar are totally default. In this case, I think that there may be some highlight on the toolbar itself, but not on the default icons.
There must be a right-click option to each toolbar, so that the user could return the default state (reset) only the selected toolbar, while the rest toolbars remain unchanged. Currently, Rhino allows to reset all toolbars, but this will delete forever any customization. Many times the intent is to reset just one specific toolbar instead.