I'm wondering if it is possible to overwrite all the unique/secret/user-specific values on a PAL NAND image with those from a Japanese one and use the newly overwritten image as emuNAND on a Japenese sysNAND 3DS.
Any insights would be much appreciated.
well, there is not any special thing about jpn->eur, so let's just talk about region changing etc.
to do a real region change, you need to change a file or two in the nand. we have nand access through the 4.5 exploit, and probably soon with gw, but i'm not sure we have everything what is needed to 'put that file back together again', so that the 3ds would read it happily.
if we were able to do that, then sure we could change the region for sysnand, emunand, have them each different regions, etc.
there is probably a way or two to get different region system titles running, stuff like homemenu etc, but it would be so hacky and weird that your 3ds would cry a bit i think.
it wouldn't survive an update, i have not tested it, i might later.
Thanks for the insights, I will look into the dev firmware stuff a bit more.
don't misunderstand, it's not 'dev firmware' (as opposed to retail fw). it's just manually installing each system file through 'dev menu' instead of the system doing it itself through the normal system update process
--i understand your question more now.
if you want to use a nand image from one 3ds and use it with another as the emunand (or even flash it to the other 3ds's real nand) - then no, we cannot do this yet.
if we were able to, sure the region would not be important at all i assume, all the region information stuff is stored in the nand.
but yes, at the moment we do not know how to decrypt->reencrypt the nand for another 3ds, i believe.
i think we can decrypt, at least part of it, but we publicly can't reencrypt yet. - i guess to decrypt we just need the 3ds, but to reencrypt we would need nintendo's keys, i'm not so sure. 
