Have Default Categories Selected

On our network ‘main’ site we would like our visitors to be able to quickly identify where the posts that are broadcasted are coming from.

This is simply done by just setting the category on the original post and that is that!

However, we want to make it easier for the sub-sites, which are schools to have certain categories selected by default. So for example. If it’s a football article, we want them to manually select the football category but we also want their school name category already be selected once they create the new post.

Any ideas on this, thanks!!!

I know it’s possible to set a default category but once they select a different category, the default will not be added.