[Admins]

Yes the server only stores one version of the
weapon, so when its updated then other players
get the new weapon script when they login again.
On servers with npcserver the weapons are
stored on the npcserver (that's why you can do
join and have server-side parts there), and when
the weapon is updated it sends the new script
to the players.
On free servers the weapon editing would be possible
too, although a client-side command 'addweapon <name>'
might be too powerful (cheating/hacking), but possible