You can't.

Normal.dot or Normal.dotm in newer versions is what is used when creating a blank document from scratch.  You can also, after having done so, reconfigure virtually everything in that document to be different, font, size, color, etc., etc., etc.

Documents carry their own attributes with them once they have been created.  No reference is made to Normal.dot(m) for an existing document.  Whatever it is you want changed is going to have to be changed on a document-by-document basis (unless there's a utility I don't know about for doing so in batch - but even then it won't be via anything related to Normal.dot(m)).
--

Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363  

The purpose of education is not to validate ignorance but to overcome it.
       ~ Lawrence Krauss