Editing FMC Airport Position for VHHX Kai Tak

Hi, I've recently purchased some scenery for Hong Kong Kai Tak and as the airport was not in the database I received some files from a friend. I've checked and edited the position in the .cfg files but when I load VHHX in the POS INIT page of the FMC it displays a wrong position which was included as a part of the file when I got it. The result is that the aircraft thinks the airport is 10nm to the west of it's actual position and I'm beginning to believe that it's impossible to edit the position of an airport. Thanks for any responses :)