As long as the rule is not surface deep and people can't just turn to coded language where x_code_word always mean some_person_of_color. People will be forced to reconsider their language and hopefully their thinking.
Would depend on the form Nextdoor racism takes. If they talk needlessly about it after the initial report like about how they've been "seeing too many of those lately" it could work. If, however, Nextdoor racism is users just reporting black people who aren't doing anything suspicious, I suspect they'd just switch to specifying race for everyone except black people.
As long as the rule is not surface deep and people can't just turn to coded language where x_code_word always mean some_person_of_color. People will be forced to reconsider their language and hopefully their thinking.