Downgraded successfuly, first try with IronHax Old 3DS on 10.3.0.28u, I loaded FTBrony, force quit with L+R+B+Down, started up sysUpdater. Even the "Rebooting in 10 seconds" worked for me. Keep in mind this was my first try, on Masher's homebrew launcher, and I never did the DeadCafe thing.