How would the plot and outcome change if Fahrenheit 451 were told from a different person’s point of view? (You choose the character and please be specific.)

Point of view is all-important to a piece of literature. We would have a very a different outcome if this novel were told from the perspective of Montag's wife, Mildred. With Mildred telling the story, the outcome would be far darker, as she would never see the alternative underground society of people trying to preserve the knowledge in books.
It's important to understand that everyone is the hero of their own drama. Mildred would see herself as the hero, putting up with an unbearable husband and having to take desperate steps.
Mildred would understand her that husband, from her point of view, is growing increasingly more crazy. After her attempted suicide, she would have settled into a routine. She would have recognized once again that they had a good life. She would have enjoyed her television shows and regained ground with her friends Mrs. Phelps and Mrs. Bowles. Finally, she would invite them over for television and martinis.
However, shortly before they came over, Montag would being to act crazily, taking out a Bible, an illegal book, and wanting to read it with her, which to her mind would be like asking her trip out on acid: dangerous, illegal, and unnecessary. What if someone found out? What if their lives were ruined? She might ask him, as she does in the novel:

"See what you're doing? You'll ruin us! Who's more important, me or that Bible?"

Then, when Mrs. Phelps and Mrs. Bowles came over and they were having such a good time, laughing and drinking martinis and watching television, Montag, increasingly unstable, would come out and try to read books to them—why not offer them heroin, she might wonder? Why go out of his way to ruin her good time? It would be up to her to save the day, to try to smooth over her husband's insanity, saying:

"Ladies, once a year, every fireman's allowed to bring one book home, from the old days, to show his family how silly it all was, how nervous that sort of thing can make you, how crazy. Guy's surprise tonight is to read you one sample to show how mixed-up things were, so none of us will ever have to bother our little old heads about that junk again, isn't that right, darling?"

And then, when he was hiding books all over the house and garden, it would be up to her to try to save herself by turning him in. She wouldn't want to do it, but what choice would she have?
Montag would be stunned, saying to her, "Mildred, you didn't put in the alarm!" but she would just walk past him with her suitcase and drive away in the car. He had ruined everything:

"Poor family, poor family, oh everything gone, everything, everything gone now ...."

Think too how the story ends for Mildred: not well.