Each level can have unique settings applied to it via the World Settings options. The World Settings options allow you to do everything from making sure the right Game Mode is activated when you play the level to allowing you to adjust how the Global Illumination will look for that level.
On the Level Editor's Toolbar, click on Settings.
In the drop-down menu that appears, select World Settings.
The World Settings panel docks next to the Details panel in the editor UI by default. From here, you can now specify the settings for the current Level.