How to easily add prism plugins to hosted (pro) account

I have a hosted account, so it was easy to add Prism syntax highlighting. The instructions had me add some injected code via the settings page:

However, I also want to add line numbers. That’s via a Prism plugin. I’m hoping there’s a really easy way to do that, but the Prism documentation is too general to tell. Is there?

(Tweaking theme zip files and uploading them counts as “really easy”, but I seek clarity about what to put where. I’m a backend programmer, so I’m ignorant of a lot of tacit knowledge about working with CMS’s. And I want to keep being ignorant.)