Wagtail includes a "settings" menu item by default, with some default settings items, such as "sites" and "redirects".
I know that you can register a new setting with the register_setting decorator, and that various hooks are available for customizing the top level menu items, but not sub-menu items. How can I REMOVE (or hide the display of) the default settings items?
Create a Wagtail group (Groups under the Settings menu). When assigning object permissions for the group, make sure Site Settings is not selected. Then assign to the group the Users who you do not want to be able to see the Site Settings menu, and it will not show up for them.