...I think I’m going to try it but I wanted to see what folks thought.
There was a time when the highest profile contributors could do this Yuri Acurs being the obvious example. I doubt its a thing in the current climate.
I am guessing that anyone that manages to get a better deal will also have some sort of non disclosure clause so it will be like fight club - the first rule is you don't talk about it. I also agree with most of what has been said before - you need something special to get a special deal.
If you have something very special that the agencies don't already have lots of, you might be able to negotiate a deal.
Given the huge size of agencies' collections, I consider the likelihood of that situation very, very low.
I once successfully negotiated from a life-time ban on the SS Contributor Forum to just 30days.