Changing Airport ICAO

Can a similar technique be used apply the ICAO code of a now closed airport to a new one? For example EGTH was Hatfield which is now closed and has been assigned to Old Warden
Default ICAO codes can not be changed. They can be moved (to your new airport) but not deleted without hacking the bgls, which I do not recommend out of experience. It can create a very glitch ridden and bug infested environment.

I do believe the default name and ICAO are permanent. You can isolate and create a new one with the same ICAO and a new name and see if it works, but I havent tried this so IDK but I dont think it will unless FS overlooks duplicate ICAO codes.

If my thinking is wrong, please correct me. I know a lot but not everything. :D