[BES418]

That is indeed annoying. Random crap like this happens more than everyone thinks. (Dealer employee here). The dealer should offer a few things. But obviously the new bumper and paint has no cost to you. If its heavy body work is one thing. A bumper is a bumper. A good certified shop will match the paint excellently and it would be the dealership to confirm this. Bumpers are plastic - the paint will never match metal panels 100.00%. Go look at astons and ferraris for this too. You will not be successful with a buy back. It is nothing mechanical. There wont even be a carfax on the car because there is no claim.
Just relax, you get a brand new bumper and roll on.
Personally, my ZB M2 was damaged in transport last Fall. I was notified. A new rear bumper was put on and painted at the port. I cannot tell the difference and appraising cars is one of my dealer roles.
If there is an open claim with bmw (not the dealer) then maybe see if they will cover a front ppf wrap or something for the inconvenience.