This method has been known for a long time (since the King Kong Exploit days) and does indeed 'work'. Basically you swap the Keyvault (or 'KV' in short, it stores stuff like console certificates, per-box private keys, DVD key, etc) inside the NAND with the KV from an unbanned console. While technically very different you could somewhat compare it to swapping eeprom data during the Xbox1 days.

However there's a really big IF (besides the required tech knowledge).  You still need the (unique) CPU key of your banned console, without it you can't correctly write (or encrypt if you want) the new KV data in the NAND bin of your banned console.

Now you wonder how to get the CPU-key?  Well by running XeLL of course! To run XeLL you need to perform the JTAG hack (or the King Kong exploit, but that's even more outdated), and if you got banned the last few weeks it means you updated to the latest dashboard/kernel (else you can't get on LIVE).  And that's the problem. Microsoft patched the JTAG hack since kernel 849x (July 2009), so no way to boot up XeLL (= no realistic way for you to get the CPU-key) and thus no way to swap the KV data in your NAND image.

And then there is also added KV protection (hashing) on newer motherboards (Falcon+ ? and kernel 1888 won't boot on those), but if you can't even get your CPU-key it doesn't matter much to do deeper into this problem. The only way it would work is if you retrieved the CPU-key of your old banned 360 before you updated to anything over 849x. If you did that you probably know about all of this and I'm not telling you anything new. Downgrading kernel is not an option either, older kernels won't boot as both kernel and CB fuses were burned during the various updates MS performed, and you can't bypass that without your CPU-key.

Hope that explains the situation some.  It would probably be pretty easy for MS to detect KV-swaps (like HW-mismatches etc).  In case it wasn't obvious yet those "unban isos" are fake and iXtreme LT won't unban you (it will instead try to avoid new bans).