Navigate to your installation folder: Steam/steamapps/common/XCom-Enemy-Unknown/XEW/XcomGame/Config/ .
Once enabled, these commands can drastically alter your campaign: Dev Console (Long War) - UFOpaedia xcom enemy within dev console full
Example: .Bindings=(Name="U", Command="restartlevel", Alt=True) xcom enemy within dev console full
You can use PatcherGUI to apply a "Developer Console Activation" patch (often found as a .txt file on Nexus Mods) to your game. Essential Console Commands xcom enemy within dev console full
The Long War mod on Nexus includes a "Dev Console" option in its misc files.