Could I potentially trade negotiation rights to manning? I believe I can.
Fair question, but we're going to say no on this. If you decide you don't want to re-sign him that's fine, and in that case we'll open him up to everyone. But the exclusive negotiating rights we're giving you on him are a special circumstance, so it wouldn't really be fair to let you trade them to someone else.
You're welcome to sign him and then trade him though.