I do this.
I have one document that holds the header and footer in bookmarks.
My templates have an AutoNew macro that copies those bookmarks into the header and footer area in the document, overwriting any current content.

You could, instead, store your header/footer as AutoText in a Global Template. Then use AutoText fields in your templates/documents. You can use AutoNew / AutoOpen macros to update those fields. That is better, IMO, than using bookmarked text.

However, someone needs to know what to change when changes are needed.

In either of these, you edit the base and it gets updated when the template/documents are used.