As far as I knew, it's not the gear that makes someone a SPARTAN X, it's the process. Therefor Chief is kinda stuck as a II no matter what.
He was a II in MJOLNIR 1-6 gear, right?
Yea but its the augmentation surgery they go through that really changes them into the supersoldier, so I assume TC means it'll be a new surgery process. Although technically each spartan belongs to the numbered group he was raised with, the number symbolizing the program he's involved in, so actually I'm not sure.