First point: On opening a document, Word always tries to connect to (that is, load into memory) the most recently attached template. (This has nothing to do with the "Automatically update styles" setting, which has a different function: https://wordmvp.com/FAQs/MacrosVBA/UpdateStyles.htm.) For your purposes, the "Automatically update styles" box should never be checked.


Second point: Before you allow external users to open the document, you should use the Templates & Add-Ins dialog to attach your Normal.dotm template in place of the originating template. When an external user opens the document, it should attach their Normal.dotm (http://www.addbalance.com/usersguide...s.htm#attached). This will not replace the document's styles (copied from the originating template at creation time) if the "Automatically update styles" box is not checked.


None of this should involve messing with the document's XML.