Style template that makes files update their style automatically
You are looking to use Word Templates, using your own template in all the documents, so that when the template changes, all the documents change automatically.
Your documents will need to defined with the new template. For making it work, you will need:
- Show the developer tab in Word
- In the developer tab, click "Document Template", Templates tab, enable "Automatically update document styles" and click OK
- To add the new template to an existing document as described in Apply template to an existing Word document file
The above modifications need to be done for all your documents. If attaching the templates one-by-one to many documents is too painful, and if you can cope with VBA, see the VBA macro in Batch Template Changes.
Look also into theme fonts.
See Changing Default Settings by Word MVP Suzanne Barnhill and my writing on Themes. You can save a custom theme with your settings. If you use theme fonts for your headings and body text, you can change them in any document using the theme by making a change to the theme.
If the theme does not exist on someone else's computer, though, I can't predict the results.