Multiplayer Modding Question

[Edi]

Both host and players must have the same updated version of the mod. Otherwise "interesting" things might happen.

Here is a thread where updating games on the run is discussed. That method has only been tested with SP games, but I do not see why it would not work for MP games as long as everyone updates the mod and restarts Dom3.

However, there is one caveat: Spell modding has never been tested with this, so I have no idea whether it affects that. I suspect the changes will only take effect on next hosting in your case.