I agree with Stefan, completely.
You want to use a particular style rather than the normal style if you want different formatting.

You also almost certainly want to get rid of the Automatically Update attribute for your normal style.

Understanding Styles in Microsoft Word

Once you have a text box formatted the way you like (including a paragraph style to format text inside the text box) you can save it, blank, as a text box building block for future use in that or other documents. Automated Boilerplate Using Microsoft Word