alot of the compustars will still retain the other remote, my remote got programmed to my buddy's car, and still is, even with doing as you recommended.
only sure way, is to get a new "brain" and program your own remotes.
even that isn't secure, as it's so easy to program another remote at a shop without the owner knowing.
if you ever get work done at a shop, and have trust issuses, than remove the brain when you get your car seviced, and plug it back in , when you pick the car up.

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