Terranort is the fan name for apprentice Xehanort.
Now that is just plain stupid.
For the MX controlled Terra, then yes, I could see "Terranort" being a suiting name, as MX hadn't influenced Terra's body yet. But for apprentice Xehanort?
Terranort is commonly used to speak about apprentice Xehanort as to prevent confusion between the names of MX and Apprentice Xehanort.
I fail to see how MX, being Master Xehanort, and Xehanort, being Xehanort, would cause enough confusion to warrant Xehanort's name to be "fan changed".