Yes, you can still do that. Go to the Niche details page (where you can see the list of actions, like when the auction ended, when the moderator elections started, etc.). Click the three dots in the top right corner. You'll see "appeal to Tribunal."
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .