Does "for once" implies that he would never make the second or third changes later?

Native speaker’s answer
Rebecca
No, not quite! Here it means "finally." Implying that it's the "only" change he has made in his life. The whole phrase "for once in [someone's] life" is quite common. Ex: For once in your life, could you please be quiet? Ex: I'm going to do something good for once in my life.