A couple of questions about suppressing posts

I went through the plugin tutorial several times, but I’m not sure exactly how it could be done. This post says that custom fields can be added to topics. If I could get a plugin to add a custom field like is_suppressed_from_digest = true to an occasional post, is there a hook somewhere in the digest code that would allow me to filter out any posts from the digest that have that custom field set to true? I don’t even need a UI but could set the custom field in the Rails console.

I don’t know Ruby well and I’m relatively new to Discourse, but I might be able to figure it out if pointed in a general direction.