Yes, it's a very simple guide - yet some people don't know how to change it.
There's two main methods;
I'll run through them both.
1. Download the attachment I have attached to the thread.
2. Use "Ban Checker/Key Checker" tab to check if you have a valid key.
3. Once you have your valid key, hit the: "Key Changer" tab.
4. Enter your key and hit "Change Key"!
NOTE: Doing it this way may compromise your key, so only change it this way if you are going to hack. If you are wanting to play legitimately, use the Manual key-changing method.
1. Go to "Run" and type: "regedit"
2. Once there, locate your Arma 2 OA folder which holds your CD Key by following this path;
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Bohemia Interactive Studio\ArmA 2 OA
4. Once there, locate the "Key" file (3rd one down inside the Arma 2 OA folder)
5. Right click and hit "Modify"
6. Enter your key and you're set!
NOTE: This can be a time-waster if you're just going to hack, this method is highly recommended when playing legitimately.
If you have any questions, do not hesitate to comment or inbox me.