
You cannot get into "Debug Menu" on 3001 Fw because it removed.
You cannot get into shell via exlink serial connection on 3001 fw too.
If you crash your device, than serial port enabled on /dev/ttyS1 on latest firmware as I remember but I am not sure about if you can use it, specially if you have CI+ device.
Normally, with other firmwares you can revive your TV via linux shell from exlink serial connection. But you cannot have this option with 3001 FW if you don't change some partitions on your TV.
For security, I advice you to take backup of your partitions (all of /dev/tbml* and dev/bml0/* devices ) and rewrite your uboot code which is deleted by 3001 FW.
With proper uboot code partition, you can boot your TV via external USB Flash. This way could recover your TV even if your root/boot partition is corrupted.
Current roll back technique is really safe because you don't flash anything. Just reverting flash via TV's own functions
