In the Civilization IV multiplayer the mods are perfectly controlled, any difference is detected and does not allow to continue, the player-server and the players of the game must have the same mod. What I do not know if it is easy to do this, the source code of this game is free, so you can see how it controls it, for those who understand programming, of course.
I have a half-finished mod, in which I leave the Dutch and Norwegian MM at 20 each. Modify some technology that is never investigated to make them more attractive. And events to prevent actions that we only do for the advantage of knowing the rules of the game, such as invading Yugoslavia as soon as possible, or Vichy only accepting the French surrender, Syria, Iraq, Persia ...
My native language is Spanish, and no English language mastery, sorry.