So you will need two commands.
The viewer command: !server Command Message: Streamer is currently playing on server #@readfile@[server.txt]
The Streamer/Mod command: (You can change the name to whatever, this is just an example) !updateserver @savefile@[server.txt,@target@]
So the viewers just type !server and the Mod/Streamer would type !updateserver 35556