If Severus could live his life again, with all the knowledge he has of what will happen and he cant change a thing, would he do it?

Of course not! Why go through such an awful life a segundo time around? Why would he want to be born poor, to neglectful parents, have only one friend, be bullied through school, lose that friend, sumali a doomed evil society, spend 20 years as a spy and die alone and as one of the most hated wizards in Britain?

I think he wouldn't chnage his life at all. With Lily he learned to love, with Dumbledore he learned respect and loyalty, and with Harry he learned to care for another in an unconvential way but in a way that still had an impact on Harry and his friends.

I'm not sure. On one hand, part of me says he would just want to live those happy years with Lily again. Another half says that that would just be torture for him.

Maybe he would, if he just could see Lily again. But... to have the knowledge of all the things (that have happened in is other life) would mean also that there must be some change, cause I'm not sure if he would do things like calling her 'mudblood' again or any sort of this. He would just shut up and that would mean that there would be an influence in his future life.

I don't think so. Like he sinabi to Dumbledore, he'd give anything to keep Lily safe. I think that would include removing himself from existence so Voldemort would not hear about the prophesy from him.