The whole point of the story is that he is black and gets treated unfairly (accused of a crime) because of that. It’s fundamentally about the racial discrimination that was rife at the time.
Take that one element away by making him white, and it remains an interesting story but now it’s about something very different, and I doubt it would be as famous today. It’s also not clear Harper Lee would have bothered to write it.
> Take that one element away by making him white, and it remains an interesting story but now it’s about something very different, and I doubt it would be as famous today.
It would be Bridge of Spies, which makes the same comments on what it should mean to be a lawyer, and on the nature of mob justice, while making the two changes that the defendant is (1) white and (2) actually guilty of the same offense he's charged with.
Take that one element away by making him white, and it remains an interesting story but now it’s about something very different, and I doubt it would be as famous today. It’s also not clear Harper Lee would have bothered to write it.