well, are we talking about just the bumper, or the whole front end? are you talking about the E90 (2006+) 3-series?

kung bumper lang, i agree with the other guys. if you want a 2003 look, well, you'd have to perform substantial modifications to the whole front end including the hood and fenders....and that's a different story (pero di parin dapat ma-void yung warranty sa mechanicals).

i would question, however, the wisdom of doing major surgery on a new or close-to-new car. if you don't like the looks of the new version, just buy the older version and save some money. or if you already have the car, look at some aesthetic mods to make it look different.