unfortunately the gauge cluster is tied into the pats system of the car, you will likely need to take it to a dealer to have it reprogramed. I don't know why ford did it like this, but I assume it is to keep pple from changing clusters to a lower mileage unit.
The PATS system is one of the biggest consumer rip offs of all time. I have seen cars that wont start after simply jacking it up and changing a tire. I wish they would have included a default reset that could only be performed by the owner, but ford decided that they need to make money at the dealer garage.
I really believe you will need to see a dealer for this issue, as the Pats module, cluster , and PCM are tied together with your key. Each one must have that key programmed into it.