Seemingly impossible. However, can I apply a new theme to a course? I have a course, this has a theme. I want to create a new theme and then apply it to the course. How can this be done?
Completely possible!
From inside your course, go to the Theme menu (palette icon on the left)
In the top right, choose “Select theme” if you want to choose from an existing theme, or Create Theme if you want to make a new theme. You can then choose which theme to use as a basis.
Very possible indeed! I really don’t know how I missed that, only to say I’m fairly new to Evolve. Thank you for your quick response! 
You’re most welcome.
We’re all new to Evolve at some point and we welcome you on your journey - and that’s why we’re here, to help you at any point of your Evolve experience, with any level or type of question. No judgment.
Do explore the Evolve Hub if you haven’t already, too… https://experience.intellum.com/student/activity/764889-content-authoring-with-evolve
Best, Helen