change default subscript impress

I use superscripts and subscripts frequently in Impress. They are too small and misplaced for my audience to read and understand. How can I change the default so that I don’t have to change every one?

Setting the default doesn’t appear to be available in Impress.
The Alternate Find & Replace extension doesn’t work with Impress, and I’d rather not do it for every document, anyway.
Superscript and subscript options don’t appear to be available under Styles.
Changing the superscripts and subscripts on the character menu and saving the document as a Template doesn’t preserve the changes.

If this requires changing an .xcd file or some other program file, I will do it. Individual changes are far too time consuming.