I don't know if the Hemingway usage captures the spirit of the times but I think the language in Huck Finn "works" --- racism is a terrible thing --- and Twain exposes it brilliantly in Huck Finn (the character of Jim is so strong that Huck cannot "pray a lie" when he tries to apologize to God for protecting Jim (a runaway) from being captured and sent back to slavery) --- and racists should use that language.
Black folks do/did too --- Read August Wilson's plays --- (I always thought the younger playwright of A NIGHT IN MIAMI reduced authrenticity when she had those four characters call each other "Negro")
WHen the TV series ROOTS was on TV it was essential that racist white folks use that language ---
WHen I would read aloud in my classes that dealt with racism, I wouldn't READ that word aloud --- but to doctor the books seems a bit silly --- It is essential to warn people about all reading, film, etc. that might seriously create flashes of pain (I guess the technical term is "trigger warnings") but the realities described in books, etc. are important.
(By the way, I always was very impressed by Mark Harris the baseball writer whose book THE SOUTHPAW introduced Henry W. Wiggen to readers --- He blanks out only Fuck and the N-word leaving bastard and other "curse" words whole --- in contrast to newspapers at the time who blanked out words like bastard but left the N-word in full print ...)