Just wanted to put this out there, for those who get the error: "You do not have permission to this command" when trying to use /npc_add I have the solution. 

You need to either be the Owner (Auth lvl 2) or a Moderator (Auth lvl 1) in order to use the mod
Input one of these commands in the console, for steamID you need to input your own ID

ownerid <steamID> [Name]

Moderatorid <steamID> [Name]

writecfg