SamyGO

Yes you guessed correct.

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

This because of Linux kernel Firmware changes and u-boot code remove. you just reversed mtd_exe partition. But still use restricted linux kernel and empty u-boot. You needed to change this partitions from your backup too.

You might find it from same TV model from your friend. You might request from some friend of you...etc.
You can also compile your kernel via SamyGO Open Embedded SVN. I also bet that you could find u-boot from anywhere

Soon, we could rewrite uboot code (that samsungs proprietary code parts) so you can load and install required uboot to your TV.
Simply with proper u-boot code, you can revive your TV even if you make really dump actions (like erasing linux kernel & boot partitions)
You can also find how uboot thing works at wiki (I am not sure if there is a information on wiki explains that really, but I guess)
If not, It will be added soon

Advanced mode is a for automating startup process of custom tools. It could mount your shares to TV, can load alternative WiFi drivers... You can also make those via hand like from ExLink or Telnet... Detailed instructions are on wiki page.