How do I alter the page title h1 tag from a module? I miss hook_page_alter()!

I want to create a module that adds some configurable markup to page titles (the H1 tag on the HTML document) for full node pageviews of certain, configurable content types. But according to this change record:


  You no longer can change $page['content'] (or, generally speaking, $page[$region_name]) into something completely different.


I know I can override twig templates to achieve this, but can I do that without creating a theme? I'd like this to be a reusable module.
The page title is now a block, so you can override its template file.