First, there’s no indication yet that they’re retconning any characters. She was announced as one of the two leads, she wasn’t announced as either Mulder or Scully (characters who may not even be in the show).
Second, this really comes across as you assuming she was only cast because she’s black. Maybe, I dunno, she was the best audition for the role? Maybe the lead character she’s playing is meant to be black to begin with?
2 things:
First, there’s no indication yet that they’re retconning any characters. She was announced as one of the two leads, she wasn’t announced as either Mulder or Scully (characters who may not even be in the show).
Second, this really comes across as you assuming she was only cast because she’s black. Maybe, I dunno, she was the best audition for the role? Maybe the lead character she’s playing is meant to be black to begin with?