I've done it before, twice but I would probably pay someone to do it now. I never felt comfortable dealing with those springs.
The installer who replaced my springs recommended I lube the springs a few times per year. He said the friction of the steel coils grinding against each other every time the door goes up and down will eventually cause the springs to fail. I've been using Amsoil Metal Protector but I would imagine anything that doesn't easily drip off will work.
Just because you can do something does not mean that you should do it. This is one of the few home repair jobs that is truly dangerous, pay the reasonable fee to have it done by someone else.