Can .map files and mods be hidden from other players in mp?

[llamabeast]

I believe you can do this actually.

Firstly the map file is easy, as the players never need that anyway.

As for the mod, what you could do is have players able to recruit extra secret things.

Host version: Includes everything.
Each player's version: Only adds to the recruit lists for their own nation. If there are any new units though, they will have to be present in everyone's version.

Using a difficult keyboard so can't face explaining why, but hopefully that should make sense with a little thought.