Your wish is my command. Put the following html tags around the text you want to be small:
<font size=1> The text you want to be small. </font>
... which gives you The text you want to be small.
Officially this is "deprecated" in the latest version of html (HTML 5), but it will be supported for a long time. The "proper" way to do it is with CSS (Cascading Style Sheets), but FR doesn't support CSS.