BMW doesn't even paint the bumpers themselves when they build our cars. A parts supplier clear across Germany makes and paints the bumpers, then ships them (painted) just in time for each car. IF you look closely the paint is slightly off. But no one really notices that.
I think as long as your body shop uses a flexible agent in the paint... and uses the OE color, you should be fine. Any good body shop will know what to do, and do the job right. Make sure they guaranty their work in writing.
