I think there is a good possibility that those parts are interchangable. They look almost identical. Even down to the indentations at the very front of the pipe.
It would make sense that the dealer does not want you to interchange parts as they foresee potential problems recommending parts from other models.
We just need someone to bite the bullet on the 135i performance exhaust for us!
(Waitlist): #1 M2CS
(Current): 2016 F15 X5 3.5xdrive - 2016 F30 340xi M-Sport
(Past): 2013 535i xdrive - 2008 E92 M3
2006 E90 325i - 2002 E46 325xi
1991 E30 325i