Do professors change their impression of a previously bad student?
Your friend needs to involve himself in department life. If he is just as invisible as his supervisor, no other professor is going to change their opinion unless they somehow get a new impression (or forget who he was).

One of the best things your friend could do is to give a department seminar if he has some interesting results to present. Make sure that it is well written and rehearsed! He should also chat with professors during social occasions, turn up at department talks and ask interesting questions; things like that.