You can save your customizations in different places.
You know you can customize toolbars and menus extensively in Word and even design your own personal toolbars, buttons, and menus. If you have already discovered the delights of customizing, then you have probably saved your customized items for use in all of your documents.
The next level of customizing is designing toolbars and menus for use in particular documents or templates. Perhaps you have one report that you have to produce every week, and it would be more usable with a customized menu, but you don't want that menu in other documents.
Think carefully about which customizations you want to save in each document or template. Do you want something available in more than one document? Would it be better to save the change for use in all documents?