Bookmarked https://david.shanske.com/2020/09/26/converting-your-wordpress-theme-for-microformats-2-part-2/. This here’s probably the best guide to “IndieWebifying” any WordPress theme! Two things: (1) You could definitely use a child theme to do this. (Pro: very few files and very little code. Con: can’t have child theme child themes [in case others would wanna build off your work].) (2) You may wanna check for existing e-content and p-summary elements, like those added by plugins—Micropub—rather than blindly add them to every post.