Changing Airport ICAO
From FSDeveloper Wiki
I know there has been various threads in the ADE subforum about how to change an airport's ICAO. I decided to write this article to have it in stone about how to do it. Below is the process for FSX. In the example below, we will be changing 45J to KRCZ.
1. Open the stock 45J (your airport) in ADE9X.
2. Delete everything from the airport except the ARP, including runways, aprons, taxiways, etc.
3. Go to File > Properties.
4. Put 0.0001 in the Latitude, and 0.0001 in the Longitude. Also, change the elevation to 0. This will place the old airport(45J) in the center of the Atlantic.
5.Save As "45J_ARP." Now you want to compile. You must compile "45J_ARP" into your Microsoft Flight Sim X/Scenery/World/scenery folder. DO NOT OVERWRITE ANY OTHER FILES.
6. Now, re-open the stock 45J again in ADE9X. All of the runways and taxiways, etc., will still be there. Go back to Properties, and change the ICAO to (in this case) KRCZ.
7. Save As "KRCZ_ADEX_(your initials.) Now compile into the default folder (FSX/Addon Scenery/scenery.)
8. You have now successfully changed the ICAO for any desired airport.