Since this change in the book was voluntary, there was nothing else said on the subject. And to the end of the book he was referred to as Vito Corleone, and his sons had this surname.
There was little trouble for FFC to change this small detail of no actual importance - HOW he got the name. But to change all the rest, especially considering that the first movie was already released and everyone was Corleone there, was certainly out of question.