to change region you should not use the 9.2 update firm cias that one uses to downgrade to 9.2 (9.1 in japonese region)
that zip doesnt contain all cias since it only has the one that were changed after the 9.2, so you can go back to that version.
what you need to do is download every single firmware the 3ds had, and stack up the cias from each newer version one after the other.
i realize this because when i changed the emunand region of a Japonese n3ds, everything worked fine until i tried to change a folder name, then it crashed, simply because it didnt have the american keyboard, which was updated for the last time on 6.0, so it wasnt alongside the cias i used for the regionchange.
so do that, get the firms from that iso site or from 3dsnus, create a new emunand and try again.