Custom Number Formatting and Styles Controlled Centrally

AJHezzleUnfortunately, you can't really edit that dropdown. Better is good Workgroup Templates which tie numbering to styles as set forth in the Shauna Kelly article along with other useful styles. Train your users to avoid those numbering options completely.

You could, as administrator, remove the numbering buttons from the Home Tab if you want, but you do need access to the Define New MultiLevel list dialog to set up your numbering.

It is possible to have a Global Template that contains numbering styles that can be imported. See A Global StyleSheet in Microsoft Word? An example can be found in my downloads: A Global StyleSheet in Microsoft Word?  Unfortunately, [Quick] Style Sets do not work for numbering.