You could but changing ignition lock cylinders is pretty difficult and will no doubt cost more than getting a dealer to provide you with the key codes. Once you have the key codes you can get a locksmith to cut you a new key pretty cheaply. I recently bought a high mileage toyota tacoma and had to have new keys made in order to get the door lock cylinders to work properly again. The only key I got with the vehicle was worn so badly that it no longer worked the door locks without a major struggle. I did have to provide the dealer with proof of ownership before they would release the codes to me. I had two keys made at local locksmith shop for less than $20 try getting a replacement ignition set for that price! Also if you go your suggested route you will still not be able to operate the door locks!