I know for sure that African-Americans reserve the right to use that word themselves, about themselves, so it becomes a gray area to quote the word and spell it out even if uttered by a person of color.

This is probably a pretty good summary of the issue: [theguardian.com]

You can usually rely on respectable media outlets for the current thinking on this because they have to struggle with this editorially all the time. Unfortunately if you believe the Guardian, the answer is, "it depends" and editors read tea leaves about it and use it very selectively in "certain situations".

I wonder if it's discussed in the various style manuals or not.

Anyway for non-professional writing it's probably best to merely suggest it with n----- or similar. It will be clear from the context and no one will have an excuse to take offense or assume you're a closet racist or something.