From what I understand, if you fit new batteries to the keyfob, you then stand near the car and press the fob button 4 times. That should reset it.
With a T4 (laptop) you can read the numbers of any key that has been used previously. i.e. when my mech was adding my new key he found two numbers already entered, but not knowing which was for the existing key he did not cancell either of them, he just added the numbers from my new key, (a plastic label was attached to my new key with a bar code on it) making a total of three key numbers..
Hope that helps a bit..
NOTE--- the new key cost me £152. And still had to be "registered" in the cars ecu (?)..
.