Are there any aircraft that come with interchangeable flightdecks?
According to this answer they used to be very customizable, but not very much interchangeable at least to the point that no one bothered to change them on second-hand aircraft. They are reducing it because it only causes confusion. Aircraft change owners and pilots change employers and it's most useful if all aircraft of the same type have the same cockpit layout.

As far as 787 goes, it has very similar flight deck to 777, always, to the point it has common type rating.