see, the car in made on ur order, the chassis number, engine number everything is bound to your order.
best they can do it, replace door with a brand new one and paint it according to color of ur car.
now it depends upon the color, if its white then it wont be detected, but if metallic then there are chances that there will be slight difference.
some say that they dont place seals on the replaced door so it can later cause suspisioun that door was replaced due to accident.
be frank with them and ask them wat the story behind it and wat r ur options.
in case disagreement, there is escalation, consumer courts and our legal system.
if u have firm evidence and sure that its a solid case, then dont have to worry abt it, you wont loose any value.
but the rule of thumb for any legal case is u have to ask for the world if u want to get a peanut.
ask for a brand new different car with 10million in damages, and expect u will get a new door free of cost, it will be a success