Sure, but from what I've seen on youtube though, it seems that they've simply overwritten some generic stadiums with the files of their 3-4 French stadiums; or they may have replaced both the generic stadiums and their menu names. If the files exist by default in RC2, however, then I assume that they have their own 4-letter codes, or folders (as it's set-up in the cmn.pak file); so it'd be a matter of adding the required lines to the .db to have the hidden French ones as "new/unlocked" stadia without touching/replacing the generic ones.

For the most part, the French stadiums certainly look like Sidhe creations.