Technically, the only legal way to play is for each computer to have a legitimate, purchased copy of the game installed. The LAN setup is really a workaround.

Anyone can host, it does not have to be you.

If you want to run multiple commands using a script, all you have to do is make a text file that has the commands in it, and then execute that script from the console.

For example, you want to make a script that executes the commands you listed in your first post:

Make a text file called LAN.CFG and put it in the C:\Program Files\Steam\SteamApps\common\left 4 dead\left4dead\cfg folder.

Edit the LAN.CFG so that it contains the following lines:

Sv_lan 1
sv_allow_lobby_connect_only 0
net_start
map nameofthemap

save the file, and then from the console you can just type:

exec lan.cfg and it will do any of the commands you put in the CFG file.

I don't have any personal information about the launcher you are talking about.