Hey there, great questions!
You can do either. The key is you need to establish the connection between the two. Once that is there, the commenting functions will work. I’m guessing you know how to do handle the “Publish to Discourse” option, i.e. when the post is created. For the linking option, you can link any Discourse post to a Wordpress Post by using the “Link to Existing Topic” publishing option in the sidebar when you’re editing the Wordpress post.
The key here is that when you have the “Show Existing WP Comments” setting enabled the wp-discourse plugin inserts the Discourse comments (i.e. the posts from the linked topic) on top of the normal Wordpress comment template, which retains all of its normal Wordpress functionality.
This means that one way you can handle this is in your Wordpress theme, by modifying the Wordpress comments.php template. You can do anything with the Wordpress comments using this approach.
However, if coding is not an option you can turn off Wordpress comment compose (or “close” the Wordpress comments) in the Wordpress Admin UI the same way you would normally in Wordpress. Go to “Settings” > “Discussion” and then:
- For new posts, uncheck “Allow people to submit comments on new posts”.
- For old posts, set “Automatically close comments on posts older than” to 0.
The upshot of this is that you’ll retain your old comments below the new Discourse comments and the Wordpress comment compose will not be visible.