In other words do you have to comply with french or EU operationnal regulations if you fly N registered heavy acft ?
No you do not.
If the French want you to comply with that regulation, they must obtain a waiver to the appropriate ICAO Annex. For example, the French banned all pilots over the age of 60 from flying over French airspace, as this was covered in the annex, all countries had to comply. (This was prior to the new age 65 regulation.)
It is also next to impossible to impose all EU-OPS regulations on FAA certified aircraft, for example how would you comply with regulations pertaining to contaminated runways?