You can try (I found the entry in another forum)
KOMBI > CC_TEMPERATURWARNUNG
It will probably say "nicht_aktiv".
Allegedly this setting is reversed from what you think it should be - "aktiv" turns it off.
I haven't tried this code, so I don't know if it disables the entire feature or just the noise. I'm thinking it disables the entire feature, but not sure.
Personally, I drive where the temperature can change by 4 degrees or more from departure to arrival - I sometimes appreciate the noise when it comes on while I'm driving to let me know I could expect wet or slushy roads to turn icy.
I do however wish I could upload or somehow NETTODAT a new Gong noise! Very bad choice of sounds.