Display the map selection screen. Then click on the following four bolts (in order) on the box in the top right that displays your name: top-left, top-right, bottom-left, bottom-right. Now press the cursor keys to select a new map.
Easter egg shrapnel
While playing a game, press ~ to display the command line and type "easter!". Then, all destroyed objects will create Easter eggs instead of shrapnel.
While in the command bunker, press ~ to display the command line and type "fubar!". Then, a jeep armed with a 1000 pound bomb will be created. A single hit on this vehicle will cause it to explode. Note: points, ranks and medals are disabled while this code is in effect.