Is using automation of removing or adding feedback against fourm rules?
The same rules apply to both bots and users.
It's not against the rules. When I came up with the crazy idea to leave a neutral tag on 160,000 banned accounts, theymos said this:
160k trust ratings... well, you're either getting banned for trust spam or you'll force theymos' hand to make some changes

Don't scare me

You made me ask theymos:
does it cause problems to the forum if a user leaves feedback to 160,000 users?
It wouldn't significantly bloat the database or anything, but the userpage would definitely time out.
Probably you shouldn't.
So this idea is off, Piggy's bot won't tag them.
But since trust pages now have pagination, this could actually work again
