You may have to turn back if they won't permit you to deviate. Or you may have a better experience, as Midnight Oil hasn't had too much trouble cruising up and down A470 at high altitudes.
I've been based in China, in and out of tier two and tier one cities and am convinced their ATC system was designed by the same people who's agriculture expertise brought on the Great Famine.
In the end, YMMV... Suggest you carry plenty of fuel and roll with it all.