Cheapest easiest way to sort the problem
Put your old key into the plasic housing that reads the code, Tape it into it so it doesnt fall out, so it reads the key everytime you turn the ignition on blar blar blar...
just hide it somewhere in the dashboard and think of it no more... that way when you put your new key in your new ignition it will read the key thats taped into the plastic code reader.
Thats what i did. Simple solution.