The case I know of basically went:
Child was called….let’s say she was called “Beyonce.”
Parents chose “Bea” as a nickname. (That’s not the name, this is just an example)
At school, they filled in the forms for a known-as name, making it clear she was NEVER to be called anything other than Bea, in speech and in writing.
As soon as it was legally possible, the child changed her name to Beatrice, and continued to use Bea as a nickname.
Parents made the right choice. Being called Beyoncé (or, in reality, an equally stupid name just like Beyoncé) is going to be utterly embarrassing and result in your CV getting binned, in the real world.