Hello! First, sry for my bad english!
I finaly downgrade my new3ds! But before it works, i softbricked another one. The softbrick was after a downgrade from 9.6 to 9.2 with safesysupdater.
I sell this 3ds and buy a new one.
On the new-new3ds i update 9.6 to 10.3 using sysupdate (from page 95)...