Theway the rules phrase the action for a given expansion map constitutes exactly the powers of the action on that map. In France the engineer allows one to build in mountains; all other players (without engineer) cannot build in mountains at all. The base three hex track-laying limit still applies for the Engineer in France.
I'm not convinced. The urbanization action description is quite explicit. I would think that engineer was intended to be 3 tiles, it would've said so. Changing urbanization to only 3 makes sense (as a change) because its usually better than engineer.