For most aeroplanes you would be correct. Mine's a Jodel, and all the ski-equipped ones that I know are on the French register. An F-reg Jodel (D140) has to have a national permit to fly (CDNR or CDNS), and can't have an EASA C of A. An identical G-reg example can have an EASA C of A.....
The French mod, that was approved by the DGAC when these aeroplanes were on full French C of As is therefore unknown to EASA.
I'm about to embark on the process, and maybe I'll be lucky.... but I'm not optimistic.