My wife and called this the "Back Porch Test". The kids' names had to be shoutable from the back porch with no embarrassment to the shouter. -Skip
As you say - - our situation was a kid deciding he'd take a new name, and had no obligation to get it blessed by a court. Hoops to jump, for us, as his supporting documents had another name (birth certificate, driver's license, etc.). My surprise was that he was correct - he didn't need a legal blessing to use his "new" name on contracts, etc.
I always thought about changing my last name to Whight, then run for public office with the slogan, "Vote Whight''.
I don't mind people inventing names for their kids. HOWEVER, they need to realize that writing letters in sequence means something to the reader. IOW - You are not allowed to invent your own spelling. ... also, I shed a tear when I run across a transcript for a high school kid named "Infant" or "Baby Girl". That kid was doomed from the start.