Hi Matt,
Sorry to see you’re struggling with a wave of spam posts.
How do you have the edit post allowed groups
site setting configured? I believe you would be able to block TL0 edits there.
Edited to add:
When I try this method on my test site, my edit is blocked by the Watched Words rule, unless I’m not completely grasping what you’re explaining. (Create a post. Click edit, replace the content with content that includes a Watched Word, submit the edit.)