Julianne Moore
Julianne Moore's story is similar to Emma Stone's. Julie Anne Smith was told to change her name because there was already both a Julie Smith and a Julie Anne Smith in Hollywood. The Screen Actor's Guild told her to try again, and she chose Moore because of her dad's middle name, and Anne for her mother's first name.
Trace Cyrus
The MetroStation singer and brother of Miley Cyrus, Trace, was born Neil Timothy Helson. He was adopted by Billy Ray Cyrus and took his last name, and dropped the name Neil for an edgier sounding moniker that suited his punk band's aesthetic.