Complex sentence: He left the screenplay with the Shah's and they called the next day to say they wanted to make the film, but wanted the lead changed from a 13 year old girl to a 30year old male, their recent discovery, French kickboxer, Olivier Gruner.
Split into simpler sentences: He left the screenplay with the Shah's and they called the next day to say they wanted to make the film. However, there was one condition: they wanted the lead changed from a 13-year-old girl to a 30-year-old male, so as to utilize their recent discovery, French kickboxer Olivier Gruner.