Goldeneye:source is a recreation of the N64's game.
By recreating a game, you guys are porting the original maps, guns, characters, gameplay, etc. on the source engine, with a little update (more polyg., better text., ...) here and there.
Does it mean you have to add new content? If it's needed by the multiplayer conversion, like the new area in backzone, why not? But a new content that's not needed/that add nothing to the gameplay, like a new gun, will spoil the original game.
So where the hell did you found a silenced ZMG in the original game?