Wot! No replies or suggestions. Either the solution is so easy and trivial, that there is no point in stating the obvious. Or, it can't be done. Well, I could not find any reference on how to mix fonts in a Text Source, so in case anyone else is looking to do this, here's what I came up with.
I want a short text message that I can use to scroll across the bottom of my live stream. And maybe I want to highlight a word or phrase in the message by using a different color or font or italics. So I created 2 Text Source entries. One entry has all the text of the message, except with spaces where I want the highlighted word, and the second Text Source entry has only that word, in a different font, or italicized, or whatever, and aligned to the gap in the first text. I put both Text Source entries in a Source Group, overlapping each other, and apply the Scroll filter to the Group, so that the start times are synchronized.
If I have missed something, or there is a better/easier way to accomplish this, I am still interested in hearing about it.
Cheers. . .