>> Now, said with a Southern French accent, it becomes [cot] <<
>> The sound I meant is [o:] as in RP or Standard British English. <<
Now you're really confusing me. Are you using IPA, or similar system for transcription? The letter "c" in the IPA, X-SAMPA, and Kirshenbaum transcription systems is a voiceless palatal plosive, that is only found in Hungarian. The letter "o" in IPA is the "o" sound in the word "coat" in North Central dialects of NAE--most dialects of England English use a diphthong for the "o" sound. The vowel that is used to transcribe the "au" in "caught" in RP is not /o:/, but is /ɔː/, the long open-mid back rounded vowel.
[cot] (I'm assuming /kot/), would be how someone from Minnesota pronounces the word "coat". It is not how an RP speaker pronounces the word "cot".
The [ ] and / / marks represent IPA or X-SAMPA transcription.
I would pronounce "cote d'ivoire" as /kot divwA/.