Hackers on the XBH forums managed to change DVD key and Game Region Code in the Xbox 360 'Key Vault' (that stores on flashchip: console certificate(s), per-box private keys, DVD key, however NOT any code-related encryption keys).
However you should know the 'Key Vault' is encrypted with the per-xbox360 'CPU key', so that means this hack is only possible on Hypervisor exploitable Xbox360s (kernel 4532 and 4548) for now. You will of course also have to read/flash the Xbox360 flashchip (by desoldering it and read/flash it with programmer or for example use the versatile Infectus dev chip)
Click the read more link to view the full article from xboxhacker.net
The Infectus mod team mailed in to let us know that they have uploaded a video of their first tests at dumpinging and and flashing the Xbox 360 BIOS NAND. They claim their mod will read and write the internal BIOS of the Xbox 360, allowing you to even downgrade!