Your point is if you could join a bounty with your trust rating?
I think it's okay if you join the bounties as long as there are no rules about your trust rating. Especially if you're thinking of joining signature campaign, you need to pay extra attention to the rules. Most cases of sig campaign won't even accepts a red trust account, but some altcoin signature campaign might accept them.

The only thing you could do to remove your negative tag is to ask the person themselves that gave you the tag to remove them. It's kinda pointless thing to do, or you could just take it or leave it the way it is. There must be a good reason behind your negative tag.

Then again looking at your tags, it's no wonder if some bounty managers not accepting you into their campaigns. Well, you were abusing the bounty with alt accounts, so... You know what that means.