As nLaunch works at boot2 level, you might be able to use it (possibly with modifications) to downgrade it I assume. But maybe there is something that I'm not thinking correctly about that would render this impossible.

Well it's confirmed that it's still possible to downgrade OS 3.9. First delete OS, then delete boot2 and flash boot2 through TTL, then use nLaunch to enter OS 3.1 and use the NandManger to delete the minimum OS information.


The full process has been post here:http://scalc.org/forum.php?mod=viewthread&tid=71

Hmmm you are right. Only possible on HW<J.

in any case : on < J models, yes.

If 3.9 is already installed, then you'd need external hardware (to reflash the nlaunchable boot2). If it's < 3.9  then it's easier.