You can add custom coordinate systems. This link may be helpful. About Custom Coordinate Systems (safe.com)
Bonsoir Charles,
From the screendump you are showing we can see that FME supports the Coordinate System with the EPSG code 2154, which is Lambert-93 with RGF93 (Reseau Geodesique Francais) datum for the whole of France métropolitaine/le territoire européen de la France/l'Hexagone.
So, why would you not use this one in your case?
If you want to reproject your shapefiles from one Coordinate System to EPSG:2154 you can use the Reprojector transformer. It might also be the case that the data is already in the right projection but without the Coordinate System explicitly set. In that case you could use the CoordinateSystemSetter transformer to assign the French coordinate system to your features, without modifying the geometry or the coordinates.
Is this an answer to your question?