Without keyboard input ( from ExLink), how could you do that? Simply you cant

If you use SamyGO Firmware Patcher, your TV will not brick. I have LExxB652 (difference is case color only) and it working good

No need to cable. If It's bricked, there is options for recover (so this step require ExLink cable.)
I don't recommend any external patched firmware. Since it's looks not legal. Buy I can say that SamyGO Firmware Patcher is tried and verified. It's working too.
Simply download the firmware from samsung and patch it. Thats all.