- The normal template should not EVER be a shared file.
- It should seldom be one forced and locked down. Doing so cripples Word use and hampers productivity.
- Train users to create new documents based on existing templates, not old documents.
I have template elements like letterhead logos, addresses and names stored in a central template that is not the normal template. That template is stored in a folder the
Workgroup Templates which is copied/updated from a central location to each user's computer as a part of network login. The macros look for the template in each user's local computer in the Workgroup Templates folder.
My other templates have AutoNew macros in them that grab parts (identified by bookmarks) from the repository file and put them in the new documents as appropriate. Since some of these templates are decades old, the finished document sometimes looks remarkably
different from the template. The AutoNew macro could easily import given styles at the same time.
However, if I were doing it over again, I would store those elements as AutoText in a
Global Template and put them in the document templates as AutoText fields. Once a document was created, the AutoNew macro would lock those fields or unlink them so the content would not change. (I am a lawyer and I want a document I prepared 10 years ago
to have the same content when I open it today as when it was created, I do not want existing documents to automatically update, only new documents.) Again, autonew macros in the templates can update the styles from that global template or from another.
As with the repository stored in the Workgroup templates folder with the bookmark import method, the global templates are master files located centrally and copied/updated locally as a part of the user login. I do not want to depend on a user being connected
to the network every time they use Word for this to work. So long as they are connected on a regular basis for those updates, it works fine, for me.
Again, my system is set up so that the easiest way for someone to create a new document for work is to begin with an existing template rather than to be working from a new document created based on the normal template. When I want to create a new template,
I open an existing template (that already has my AutoNew macro) and copy content into it. All of my pleading templates are set up to automatically update the styles in a new document from a central repository.
Using AutoText stored in global templates and AutoText fields in document templates allows a high degree of uniformity of content that can easily be updated in all templates. The same could be said of updating styles.
Your original question asked about existing documents. Again, that is not something I face because (1) historical authenticity is important to me and (2) I base all new documents on existing templates, not old documents.
Automated Boilerplate Using Microsoft Word
Unfortunately, Microsoft has over the years devalued custom templates and made it harder for users to intuitively
access them. See this article for ways to make it easier: File New Variations in the Versions of Word
It is also possible to have a template other than the normal template be the basis for new documents by default without hampering the use of the normal template as a local scratchpad. See
Easy New Document Template Package for ideas.
Finally, I have a custom Ribbon tab that produces 95% of my documents. Greg Maxey helped me develop it and I'm sure he would be willing to work with your company on a plan to implement something similar. Many of the menus on it are dynamic so that I can
simply add a template to a folder and it will show up under a menu.

Such a custom ribbon is not a minor undertaking to set up, but it is easy to maintain. It is in a global template. If you do one, you should expect to either spend substantial time on it or to pay someone to help.
Time for me to go to work!