I have done this using AutoText for the information and AutoText fields in the templates that hold the information. When a new document is created based on the template, the fields update.
Automated Boilerplate Using Microsoft Word

When I did it, I used three separate Global Templates for the data. One held the information and logos applicable to the entire firm, a second gave information about the regional manager (name and phone), the third was for the local office (local manager and assistants, phone number, and fax). Each letter template drew from each of these. It was relatively simple to change the logos and information for any part of these.