Modifying the QAT is much easier.
Modifying the Quick Access Toolbar (QAT) in Microsoft Word
Modifying the Ribbon using XML can attach to a template. It is very rewarding when it works but is such a PITA in general. I use it in regularly in
Global Templates, but not document templates. I regularly add QAT mods to document templates and even documents.
I had multiple custom toolbars on all sides of my Word screen in Word 97-2003 and still miss that flexibility.