A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
It turns out that it's not so difficult to modify existing Font themes.
They're stored in:
Macintosh HD:Applications:Microsoft Office 2011:Office:Media:Office Themes:Theme Fonts
Whew!
Make a copy of one of the existing XML files in that folder, then open the copy in any capable text editor. I've added extra linebreaks to make it easier to read (this won't affect how it works in PPT).
First thing is to change name="XXX" to the new name for the font theme (it might have to match the file name; I wasn't sure but to save some dancing around in case it's important, I made them match).
Next, under both majorFont and minorFont, change <a:latin typeface="xxx"/> to make xxx whatever typeface name you want. It must be spelled correctly, of course. If you want to change the typeface used in East Asian languages (Japanese, Chinese, Korean) you can also change <a:ea typeface="xxx"/> to something appropriate.
majorFont controls your heading fonts, minorFont controls other text.
Change nothing else, save the file.
If PPT was already running while you made these changes, you'll need to restart it to make it recognize the new theme file.
That's about all there is to it. I now have two new themes, HorriblyUgly and OnlySlightlyUgly. You don't even want to *know* what fonts the first one uses. It'd burn your eyes. ;-)
But here's an example, my brand new OnlySlightlyUgly font theme.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<a:fontScheme xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main" name="OnlySlightlyUgly">
<a:majorFont>
<a:latin typeface="Arial"/>
<a:ea typeface="Arial Unicode MS"/>
<a:cs typeface=""/>
</a:majorFont>
<a:minorFont>
<a:latin typeface="Times New Roman"/>
<a:ea typeface="Arial Unicode MS"/>
<a:cs typeface=""/>
</a:minorFont>
</a:fontScheme>
Now in theory, you could also copy an existing THMX file, unzip it, find the bits inside that affect the fonts and edit those, it'd be tedious. Instead, it seems that you can apply your edited font theme, as above, then use the Save Theme button to save as a new theme, which then appears on your Themes tab and voila, includes the fonts from the edited font theme xml file.