The Motion Picture Association of America, always resistant to changes to its movie ratings system under its previous chief, Jack Valenti, is now planning to make some key alterations to the system, Daily Variety reported today (Wednesday). The trade paper said that the MPAA will now warn parents that some R-rated movies are not suitable for younger people -- whether or not they are accompanied by an adult. Another change will allow a filmmaker to cite scenes in another movie when appealing a severe rating. In an interview with Variety Dan Glickman, who succeed Valenti in 2004, said that the organization had been influenced by criticism of its ratings system presented in the documentary This Film Is Not Yet Rated, which debuted at the Sundance film festival last year. Glickman plans to discuss the new revisions of the ratings rules with independent filmmakers attending this year's Sundance festival, which gets underway on Monday, Variety said.