I was able to customize menus with the Joomla 1.5 versions of MC. ("copy the rtmenuhelper.class.php from the rt_missioncontrol_j15/lib folder..."). But now that I try to do something similar with 2.1, I'm not finding the same solution.
I found that I could add items directly to lib/menu/tmpl/default_enabled.php, and my changes would show on the menu bar. I copied that file over to html/mod_menu/ and then the new file overrides the previous one. But when I try to access Mission Control or some other extensions, the page would announce a php error. The error occurs in the file lib/menu/default.php and the line (22) is the call: require($fullpath_menupath);
I did not find a recommendation for how to customize the menu for the 2.X version of Mission Control. Is there documentation or a recommendation for how to do this?
Make sure you clear the admin cache if you are not seeing changes. If you get an error, most likely you messed something up in your modifications. I just tested a lang change and it worked fine.