I have tried three attempts based around the payload station dataġ. I drop the fuel mass by 5000kgs and the current loaded weight reflects this. This does work and is reflected in the current loaded weight. So far every offset I have written to for payload has resulted in a re-read of the 'Current Loaded Weight' offset (0x30C0) coming back with the same value.
Im trying at the moment without success to set the aircraft payload on FS2004.