when I have absolutely no clue who would be able to assist with this, when I was reading your message, a notion did come to me that could be able to help. How will the relevant authorities determine whether or not the vehicle comply with the Euro 6C standards?
Do they test it (that is, measure real exhaust emissions from the tailpipe), or do they depend on the information that the manufacturer provided during the homologation process when the vehicle was brand new?
If they depend on the homologation provided by the manufacturer, then "detuning" it may not be adequate. Best of luck with the importation of it.