I can also verify that the same method I used before to flash PR1.1 (and is reproduced in the first post) worked to update to PR1.2 Open Mode.
1. Obtain the firmware (for me, that meant extracting it out of the N950 one-click flasher) and the open kernel
2. Back up the device
3. Power down the device
4. Start up the flasher, connect the device, go through the two steps for firmware+kernel, let the device boot
5. Set the time zone, etc
6. Settings -> Backup -> Choose pre-1.2 backup -> Restore
7. Accept some terms, enter some passwords, update some software...

I had some problems; I had to turn developer mode off and back on to get it to load the dev mode apps, and other small problems... But all in all, a very straightforward upgrade.