This policy setting can prevent users from customizing both the Quick Access Toolbar and Ribbon through the user interface ...

This policy setting can prevent users from customizing both the Quick Access Toolbar and Ribbon through the user interface (UI).If you enable this policy setting, the following UI entry points are turned off: the Quick Access Toolbar and Ribbon tabs in the application's Office Center dialog box, and the Quick Access Toolbar and Ribbon customization options on the right-click menu on the Ribbon.If you disable or do not configure this policy setting, users can customize the Quick Access Toolbar and Ribbon through both the application's Office Center dialog box, and the right-click menu on the Ribbon.