Back in September of 2017, Bing Ads rolled out account level ad extensions. With that, advertisers were able to assign an extension across all the campaigns in an account. There finally is going to be support for them in Bing Ads Editor.
Looking at callout extensions, advertisers will be able to associate account-level ad extensions in Editor as shown in the following screen:
Just select the account level in the navigation, which can be found in the upper right to access account-level extensions. Just like with shared library updates, account level ad extensions associations are always posted, regardless of if all campaigns or selected campaigns are being posted.
In the near future, support for other extensions for other extensions at the account level will be rolling out.