Just pitching in with my two bits' worth as a lawyer. Paul is right. You should be changing templates, not existing documents. Very real legal ramifications changing archive documents. Documents that you have sent to others should not be changing, even a
logo. They should stay as they are until purged.
If you are using documents rather than templates as the base for new documents, that is a separate problem you should address now.
Templates in Microsoft Word
If you set these up to be templates, you could use a central repository of AutoText entries to hold various components and use AutoText fields in the templates. That way, you could easily make global changes by changing the AutoText. If you are sending documents
to people who do not have the AutoText, you would want to unlink those fields. This unlinking can be done easily with a macro. (Generally, though, you do not want to be sending word documents out; send pdf instead.)