I have just skimmed through this thread and there does not seem to be any mention that the mileage get stored in the dash clocks to he ecu, so if you change the dash looks you need to change the mileage some how, or not as the case may be.
I have tested this by swapping my dash clock for another st with lower mileage on it just to test it and the mileage changers.
Just thought I would point it out.