My child theme has changes to at least several pages. I want to experiment with different themes and not have to keep replicating these child-theme pages for every theme. Is there some slick way of doing this that I’ve managed to miss? (Slick = no plugin, but I’d consider one if that’s the only way).
If your theme is a block theme you can define theme styles and then just change the JSON values for each style.
This might give you a good idea of how this works.