I really want to do this someday, so this response will be in your favor. Since everything on my runner is murdered out, why not?! But a few key points.. this shit is risky as hell. You have your fair share of good drivers and bad drivers. Even good drivers that just may not be paying attention and rear end you because they are too dark. So obviously gotta watch it there. I have been considering this though whenever the anarchist in me comes out and will be using a temporary tint like smoked plasti-dip. I don't want it permanent just incase I do want it off or if I would like to modify it, depending on my preference. I will go ahead and recommend that you install upgraded brake LED's first, and even a brake light strip if it concerns you. But do pay attention to the area you live in, your laws, and a method of tinting.
If you do decide to do this, lemme know! I am very interested in a project like this and I know it'll come around to me someday. Good luck!