A difficult question. I don't believe in morals and somebody deserving something. I believe nothing is right or wrong, and the only way I would kill is if I myself want to and feel it right to, according to my own (admittedly personal) reasons and values, morality aside. So, no. I wouldn't be an assassin, because I can't guarantee I will actually want to kill the mark. And if I want to kill a certain person, I don't want to take a contract on it, because that would bring another person - the client - into it and the kill would feel less of my own, and would no longer be my secret.
If you could change some part of the past, would you do it, knowing that there is no telling (by mortal means) how that would change the world from then onwards?