hmm very interesting! since these have been decrypted, I would assume that SETool is able to flash an unsigned custom built ROM as well (judging by my experience with Sony Ericsson in general, tools like SETool are able to work around any signing certificates / checksums / etc to flash firmware, enabling people to create patches in assembler that alter the firmware on the device)
But, with the Android world, I could be completely wrong. But I hope I'm not!
if this does work, then I really hope someone sets up a service to use SETool with usb-over-network so that we just buy a credit and use our USB cable and some client software to do this.. it's way too expensive if we have to buy our own SETool box + card.