I think you could just serve the heavenban content to anyone directly searching for the username that's been heavenbanned, and serve their incognito session a heavenban cookie for the remainder. No one looks up trolls except the trolls themselves. It's a lot more work to sift through an entire subreddit looking for particular comments.
No, but the troll will search in posts they've commented on and see their comments aren't showing up. Permalink the parent comment and copy that into an incognito window, and clear your cookies to get rid of the heaven ban cookie.
What you're suggesting is already implemented on Reddit. If you look at a user's page it'll show their shadowbanned comments. But if you click on the "show all comments" and view the whole thread they won't display. Reddit can't detect when you ctrl-f on a comment thread.
