Dunno if you need to do all this shit but it works.
Go to your \Steam\steamapps\common\left 4 dead\left4dead\ folder and back up this files (or not)
gameinfo.txt
steam.inf
Open gameinfo.txt, search and change:
Code:
game "Left 4 Dead" // Window title
to
Code:
game "Left 4 Dead 2 Demo" // Window title
Code:
SteamAppId 500 // This will mount all the GCFs we need (240=CS:S, 220=HL2).
to
Code:
SteamAppId 590 // This will mount all the GCFs we need (240=CS:S, 220=HL2).
Save and close.
No open steam.inf, search and change:
Code:
PatchVersion=1.0.1.5
ProductName=left4dead
appID=500
to
Code:
PatchVersion=1.0.0.0
ProductName=left4dead2[B]demo[/B]
appID=590
Save and close.
Launch left4dead.exe
Happy trolling and say hai to all the elitist morons who think is cool to make something and just keep it to themselves.