So, I bought a new ArmA 2 OA account on a different steam obviously and got the clean CD key. I proceeded to uninstall ArmA 2 and reinstall it completely to reset it to be old, banned cd key.
Furthermore, I got my key and replaced it in darky's cd key changer and then hit deny so steam couldn't update the key on the account I got banned on.
My problem is that, this banned key here:
WILL not change when I change it with darkys therefore my cd key isn't changing - but it says it is in the registry editor.
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That's because your CD key is based on your steam id, so you can't change it localy.