I'd create a new master pages based on your new look, and use those going forward. That way, they won't affect your existing work. But, frankly, best practice would have been to mostly finalize the look before beginning, have only things that will not change per page on the Master, and use Styles on everything (Paragraph Styles, Character Styles and Object Styles) to make global changes easier. **Never override styles - create a new style for each new type of text.**
It might even be worth your while to begin again with these concepts in mind. It might not seem like a big deal now, but when you are ready to update the work, you'll be glad you took the time.
Thank you so much SRiegel. I'll create new Master Pages. I will also read any chapter I can find on Styles!
With text styling, use Paragraph styles, and for any necessary overrides (superscript, bold, italic, etc.) that will affect small portions of a paragraph, set up Character Styles that contain the override only. That way, if you change the main paragraph font, your character styles will keep the paragraph font, while maintaining the bold, italic, ect.
Come back to this board often - there is a ton of helpful advice to be found from the users here.