I hadn’t considered the child theme idea. I’m still new to WP and do lots of code writing, so my first thought was straight to “make an edit.”
I may do that, but I don’t see a downside to letting the admin do it by default. Because it is an admin-only function, it seems that allowing HTML code should be allowed.
I don’t see CSS as being an option because the code is output in html-encode form. So < is turned into < and so on. Maybe with some fancy javascript, but that seems silly to me when the other solution is so simple.