Well I didn't have to go that route a goggle search brought up this post from Anton Tomov at Broghthand from back in 2003;
The problem with the downgrade from PPC2003 to PPC2002 is the fact that the ROM update utility which comes with the PPC 2002 checks the ROM header of the image you're trying to upload to the device and denies the update if you are trying to upload an older ROM. The solution to downgrade to PPC 2002 is simple:
1. Use a hexadecimal editor and remove (cut) the first 32 bytes from the PPC 2002 ROM image (.nbf file)
2. Use the ROM update tool that comes with the PPC 2003 beta to upload the modified ROM image to the device
The ROM update tool that comes with the PPC 2003 uploads raw ROM images (it does not check the header and the version info contained into the header). This is why the first 32 bytes of the PPC 2002 ROM need to be removed. The original ROM updater reads the header (first 32 bytes) and then uploads the rest of the image to the device if the version info is correct.
You have to be extremely careful to remove exactly the first 32 bytes from the image.
Cheers,
Anton
__________________
Anton Tomov
Lead Developer
http://www.antontomov.com
anton@antontomov.com
Let us know if this works for you.