Design advice for custom text pop-up menu?

The standard text pop-up menus can be customized (without modifying base classes) easily by replacing the contents of TextEditorYellowButtonMenu.  The read only menu pop-ups are a different story however - they are answered by the TextEditorController class method readOnlyGroup, which does not use a similar class variable (I am using VW 7.9).  I can add the class variable TextEditorReadOnlyYellowButtonMenu in an extension, along with suitable initialization methods, but don't see a way to hook it in without modifying the base class method readOnlyGroup.  Can anyone suggest a way to do this, or do I need to just modify the base class (and is there a preferred way to go about applying base class changes from Store)?

Thanks for any guidance in this, Steve

Just read the section on overrides - should be just what I need - only had to override the one method