I have just learned that Jennifer Lopez is having second thoughts about accepting a starring role in the upcoming motion picture version of the TV series Dallas — so much so that she just changed talent agencies. The rumor spread around Hollywood Friday that J-Lo was leaving ICM and hiring the William Morris Agency. Now I’ve found out why: the actress and her managers at The Firm believe that her appearing in the remake of the oldie-but-goodie primetime soap is a “bad move’ for her acting career. It’ll be interesting to see if J-Lo tries to un-entangle herself from the project, which is still in pre-production. Latest reports had Lopez accepting the juicy role of Sue-Ellen and John Travolta playing her husband JR. Lopez will be repped by WMA in all areas, including her music career. J-Lo has a recent history of changing talent agencies (and managers) as often as she changes outfits. (This was her third time at ICM; she’s been at Endeavor and CAA, too.) She’s the second major Hollywood actress in a week to leave an agency: as I reported the other day, Exclusive: Angelina Jolie Fires CAA!