Add all your default menus at the top of your module's menu. Order them from the menu with highest access rights (manager menu) to the one with the lowest right. Add a groups tag to each record to limit access. When a manager logs in your default menu entry will be at the top and that is what he will see. When a user logs in that entry won't be available so they will see the one below it. To order the menu items use the sequence attribute. 

<menuitem id="manager_default"
    name="Default Menu for manager"
    parent="YourParent"
    action="YourAction"
    sequence="4"
    groups="YourModule.ManagerGroup"
/>
<menuitem id="user_default"
    name="Default Menu for user"
    parent="YourParent"
    action="YourAction"
    sequence="5"
    groups="YourModule.UserGroup"
/>