I have downgraded 6 NEW3DS from 10.3 to 9.2
I have downgraded a number of old3ds too.
NO BRICKS.
I use the SULIB version of sysupdater. the first update tusxh made.
I also can run downgrade on about the 5th try or so. using MENUHAX/FTPBRONY (b exit) and than sysupdater run.
It never...