I can't give you an "official' answer, but....
Heat shrink is a wonderful thing. I've used it many times to restore insulation that was "cooked" by the light having too bright a bulb in it. I've used it to replace other damaged insulatio, as well.
I've installed fixtures that called for hi-temp wire in the past; my preferred solution is to have another junction box nearby, well away from the heat, and transition there to a higher-temp wire.
I assume that you're dealing with existing wiring. I would be willing to try using heat-shrink tubing; I'd also want to have the stuff extend well into the conduit, beyond where I can 'shrink' it.