Interesting - I wasnt refering to the 24 bit code but the Flight ID (another 7 characters) - the installer can default this to the reg of the airplane , but this can of course be set to anything under pilot control. In Aus they had great problems with incorrect settings until they got the "pilots trained".
Edit: "The Aircraft Identification transmission must correspond with the aircraft identification specified in item 7 of the ICAO flight plan, or, when no flight plan has been filed, the aircraft registration." extracted from EUROCONTROL Web site - so in the absence of any setting we should be sending our reg! (this is also know as the Flight ID)
It would make sense for the reg to be the default flight ID for GA traffic. They can track who we are anyway - but I would pref that they can address me on the radio directly even if I havent gone thru the squawk setting process yet. (Cant think of an instance that it would have helped - but just like the fact that they could differentiate quickly and address the correct people).
Very worrying that the 24bit code can be overwritten! As for the conspiracy theory I always find it amusing
( as you point out with number plates) that the average nice guy is actually the one that carries the can, but the guy they need to track can avoid it with ease!
They already have access to the tail number via the G-INFO site. Just enter the hex code - now I dont think it would take a genius to automate the web site post and auto tag the radar!
It also strikes me that using mode S properly they would not need to use sqawks codes - simplifying the radio procedures.