It's my understanding that if you intend to apply Temperature Error Corrections to your altimeter to, either, a FAF crossing altitude, procedure turn, or missed approach altitude, pilots must advise ATC of their intention and the correction that they're applying.
Pilots may refuse any IFR assigned altitudes if temperature error will reduce obstacle clearance below acceptable minima. However, once an assigned altitude has been accepted, it must not subsequently be adjusted to compensate for temperature error.
TCF