About the only legal hurdle here (somewhere in the US) is filing a form and paying a fee. You can also go by an alias, but most forms will ask something like "Have you ever gone by another name?" That would be employment, credit, bank, financial things. In other words, I could start calling myself "belfpala" in real life, but I'd still have to reveal my given name.
Cyanide is a pretty nice name tho.
Please tell me that "Lady Justice King" is a title and not her name, if it was, she would have no right in banning this woman from using Cyanide for her daughters name.
“A man will contend for a false faith stronger than he will a true one,” he observes. “The truth defends itself, but a falsehood must be defended by its adherents: first to prove it to themselves and secondly, that they may appear right in the estimation of their friends.”
-The Acts of Pilate.