Have you ever changed your first name or perhaps the name of one of your children after they've been registered and for what reason? I recently found out one of my neighbours, Mary, is actually called Eva. When I was doing my family tree some years ago, there were so many who had changed their name, I couldn't believe it. Made it really difficult to find some people.
One branch of my family changed their surname in the 17th century. From what I have no idea.
Another ancestress of mine changed her details to suit herself. Normally at the time of her next wedding. I've found five so far. She must have really liked wedding cake.
Two of my Italian aunts changed their nicknames...one changed her given name. From Filomena to Fay as she'd always been known as Fanny...yeh, yeh, I know.
The other, named Florence, known as Flossie, asked to be called Flo.