I don't know, I wasn't born then. According to this Wikipedia article about Enid Blyton, "Negro" was the standard formal term and "nigger" a relatively common colloquialism. From what I've read, even in the '70s Awdry initially resisted the change.
Awdry also wrote a line about old-fashioned corporal punishment in one book (Edward the Blue Engine IIRC). "The naughty boys were soundly walloped by their fathers". (And this is from a man of the cloth!) As far as I know, this line remains - it's certainly present in my copy of the complete collection bought in the mid nineties. As the focus for children has shifted to the TV show and the toy franchise, the original books have been left alone. Blyton's books, however, have been extensively edited - by others after her death - for modern reprints (e.g. golliwogs in the Noddy stories replaced with goblins).