No, there are no instructions yet. I think nobody went that way before - as geekmaster already said, I was playing with it. But I haven't got far, in fact I only checked whether ATK was working in principle. I tried reading from the MMC, but failed. That was probably due to a not directly readable section on the flash memory, but I did not investigate further.
It's not for the faint at heart. In the best case, this mode can be used to flash firmware. But nobody tried yet. And it's all but sure. Maybe it could be used to stage a bootloader that brings up a system in RAM only. Again, not tried yet.