User scoped settings are just that, settings that an individual user can change and will only be saved for that user.
The application scoped settings will affect all users but they are not designed to be changed by a user.
You might want to consider a different approach to storing settings that you want users to be able to change but to affect all users of an application e.g. the Windows registry or an external xml file.
Another option is to use user scoped settings but to change the location to a centralised location so that all users use/save the same settings. See Store user settings into application folder for an option on how to do this.