I am a lawyer.
Using styles and the StyleRef Field will do 90% of what you want, if not more.
Use a character style for something you want to go in the header.

• StyleRef Field
• The Importance of Styles in Microsoft Word

If you are using Word on a regular basis, you owe it to yourself to learn more about how it works.

• Basic concepts of Microsoft Word: An introduction by Shauna Kelly, MVP