In Fahrenheit 451, how can Guy get back in the good graces of the fire department?
Those are two possibilities, but it's also worth considering that since he hasn't admitted his guilt, when the firefighters show up at his doorstep, Montag could burn his house down without comment or without doing further wrong. Of course, he doesn't do this, and he makes his situation even worse by committing the acts that he does (killing your boss will have that effect on you, even in a dystopic novel) and he has to go on the run.
A further point is that Montag doesn't really even know, until the trucks arrive at his address, that he's not in the good graces of the fire department, though we get some clues. Had he been explicitly warned, Montag might have acted differently, as he doesn't seem too aggressive a character until he realizes he's in danger. For all we know, he might have reformed his ways and given everything up to stay in society.
He can stop smuggling books. He can also turn in professor Faber and go back to relishing the book burning.