You will need to be a first class hacker to use a used control unit. The control unit marries the chassis number on the 40th key cycle once in use. This can be reset indefinitely untill it goes once to 40, then its married forever.
Some of the rebuilders can clear the coding but it is not a factor handled with factory tooling. The dealer can't do it.
I bought a bunch of controllers on ebay for a song due to this and traded them to a rebuider to rebuild (unlock) one for me. I keep it as a test tool. Fits an amazing number of cars. The rebuilder I use is
http://www.beckmanntechnologies.com/