I do not think that it would be illegal for a female to play the role of Boy George in a movie. Many other females have done so in the past. For example, in the movie Peter Pan, several females played the part of Peter including Nina Boucicault, Betty Bronson, and Sandy Duncan. There were other reasons why these females played the role of Peter (lightweight for easy lifting) but they were very successful at playing the role of a male nonetheless.

Boy George had a lot of feminine qualities so a female playing his role may be a good thing. It may be very difficult for a male to do so.

"Boy George helped give androgyny an international stage with the success of Culture Club during the 1980s."  Due to this, I think it would be exceptable for a female to play him in a movie about his life.  I do not think it is illegal for a girl to play a boy in the movies, as many have already done this.  The movies where girls have played boys have even been successful.  I think it would make since for a girl to play him because he was so effeminate.  It might be difficult for a male to play the role with the feminism needed to be successful.