Custom post type support for News Sitemap?

Yes this has been requested a few times already so I will think about adding it soon.

You can always override the default post_google_news.php module to use a custom post type, btw.

Ah. That would do the trick. How might I override a module?

You can try this:

https://betterwp.net/wordpress-plugins/google-xml-sitemaps/#module_api