What I can find from reading various manuals is: -
Dash panel stores the odometer reading. This can be adapted once only and only by adding miles.
If your second-hand panel has more miles on it than the car you are installing it in, you have to accept the greater mileage. If it has less miles then you must correct the mileage or you are guilty of clocking the car and will be prosecuted when found out.
The panel has to be coded to match the cars engine, country and equipment fit. Service interval, fuel gauge and consumption indicator functions all need to be reset. In some cases the radio anti-theft will need recoding.
The immobiliser control unit is part of the dash panel, and will need to be adapted to the ECU and all the keys will then need to be registered with the new immobilser control unit.