Complex sentence: Mrs. Yule suggested the stage name of Mickey Looney for her comedian son, which he altered slightly to Rooney, a less frivolous version, which also did not infringe upon the copyright of Warner Brothers' animation series called Looney Tunes.
Split into simpler sentences: Mrs. Yule suggested the stage name of Mickey Looney for her comedian son. He altered this to Rooney, which did not infringe upon the copyright of Warner Brothers' animation series called Looney Tunes.