just to report - everything went smoothly - product code changed, firmware downloaded, N9 backed-up, PR1.2 flashed...

download firmware for product code You want using Navifirm

to change product code see:
http://talk.maemo.org/showpost.php?p...6&postcount=41

to flash N9 with the new firmware see:
http://blog.makesyouhappy.org/?p=202

(just one addition - after entering "flasher -F FIRMWAREIMAGE.bin -f" and getting the messag that system is waiting for the device, You should then connect Your *switched off* N9 to the USB port, and the process starts)

my N9 is now PR1.2, backup restored... \o/