It is not possible to use the % ... % approach, but you can indeed use a custom font on a per-clause basis, with custom styling for that clause.
Tip: graphic & font-heavy documents that would at the same time be light on legal content / legal customizations, may sometimes be better served by creating DOCX-based documents, because of the entirely different approaching (“top-down” from a template that you slighlty modify, instead of “bottom up” by stacking clauses into an empty document). We still have to document this top-down approach, but it’s not that different from how ClauseBuddy’s Smart Templates feature works, so you may want to check out https://help.clausebuddy.com.