Outlook: Changing Fonts in HTML Stationery

How can I change some of the fonts in the third-party HTML stationery I use with Outlook?

Stationery is actually an HTML file that contains font information, background and other graphical elements, and layout components such as signatures. Microsoft Office installs stationery in the Program FilesMicrosoft OfficeStationery folder. You can create your own stationery or download it from many sources on the Internet.

You specify fonts in stationery by using the HTML