Not able to add custom metadata properties to news repost/News Post from external Source in SP Online

I have a requirement to add custom metadata properties to news created from external link in SharePoint Online News webpart. So that content managers can tag/categorize news based on metadata properties.
By default, when news created from external link, it picks only Repost Page content type.
Ultimate goal is to create a custom content type based on Repost Page content type.
So that when creating news post from external source or link, custom metadata properties can be associated.
Note:- We have over 200 site collections and modification to OOB Repost Page content type is not recommended.
Any help will be greatly appreciated.