Some bounties still accept negative tag members but IMHO it's just useless to join on these campaigns because they will turn into scam at the end so all they were looking for more exposure about their project name to make more and more money as possible.

And no one can be able to remove your tags only the person who left on your profile can review it and remove it if they consider if you changed but for abusing bounties with alts then probably you are going to live with this negative rating for forever.