I went to my local dealer again and I saw flat black (very deep dark gray) colored muffler tip equipped in new 2008 550i with sports package..
I wonder this tip can be retrofitted to 2005 545i with sports package...
anyone knows about it? ??????

 

Although I can't say for sure, my guess is that it's a likely swap. The tips just slide on (obviously with some force from a rubber hammer or something) so if the exhaust pipe diameter is the same (or close) between the two cars, you might be in good shape.

There's enough exhaust mod guys here who probably know more so hopefully they'll chime in...