The press was DEFINITELY informed about the substitution of Joan Crawford for her daughter.
I live in Mississippi, and the evening (now defunct) Jackson Daily News had it as a new article on the front news page one afternoon prior to the airing.
According to Christina Crawford's book, Joan Crawford had her publists call all of the important people in the publicity business to let them have the story and to insure that the public knew.
But, it really was not a big thing around where I live. Your initial post makes it sound so major, but, really, it was not.
I think that there was as much publicity (although admittedly not a news story on the front page of the newspaper) when Troy Donohue joined that same program as Keifer.
And, I did watch the show at the time. However, I was at school during the time, and I did not get to see any of the episodes. But, my mother did, and she said that Christina was much better.