The ITCS takes precedence over the GCR for anything it specs, it does not replace the GCR in its entirety. Thus, anything mandated in the GCR but not mentioned in the ITCS is also mandated for cars prepped to the ITCS And, when conflicts exist between the GCR and the ITCS the GCR defers to the ITCS.
For example, if the ITCS specifically said cages and handheld fire extinguishers are not required, then it would take precedence over the GCR requirement for cages and fire extinguishers. It's how IT racers get around the FIA certification requirement for fuel cells.
So, since:
- the ITCS takes precedence over the GCR for anything it calls out/conflicts, and
- the ITCS specifically states "[o]ther than those
specifically allowed by these rules, no component or part normally found on a stock example of a given vehicle may be disabled, altered, or removed", and
- it is illegal to the ITCS to disable, alter, or remove any part not specifically called out in the ITCS, despite being allowed in the GCR, then
- the ITCS overrides the GCR allowance for cryo treating.
Ergo, cryo treating of brake rotors is illegal.
Like I said, in reality it's undetectable, and personally I think it's all hoo-ey and money wasted...but
...
GA