I believe (and as I have no sources to quote, believe is the operative word
here), the change of ID to the ICAO format is mandated only when the AWOS is
disseminated in the form of a Metar.

Coatesville, PA (40N), which by the way this month has installed a new AWOS
machine, transmits the weather information on 126.25 and is not available via
FSS or any other weather briefing medium. (At least, not yet.)

G. Lee