Yes your Xbox will be banned from Xbox Live once you connect to the internet.
You can basicaly buy an unban, formally known as a "keyvault". its a new key that isnt banned that you put into your xbox.
You can NOT jtag the new xbox's.
And im pretty sure you can remove the jtag by unsoldering the cables and restoring the NAND, but since you cant jtag, you dont have to worry (: