Chicken and egg here. It is really hard to renegotiate an existing employment contract. So you need to find a new job to negotiate one. But you want to have a different employment contract to make it easier to find said job. See the catch?

That said, most employers will not actually bother to negotiate with you. Many people just strike a bunch of crap out, sign, turn that in and hear nothing then think that they have negotiated. Unfortunately nothing makes the employer sign to that revision. So now you don't actually have an employment contract. Guess what? That means you fall under the default rules, which means in New York that a professional employee who is a programmer who writes programs in personal time on a personal machine is creating works for hire that belong to the employer. Congratulations on your great negotiating strategy. It earned you..nothing.

While negotiating can work, it is a lot more risky and a lot more work than having the good luck to live somewhere with saner rules.