Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. Locate the "game.pak" in game folder and use WinRar or a similar program to open it. Extract the "lod.reg" file in the "Registry" folder to the Desktop. Use a text editor to edit the "lod.reg" file as follows:
Save the file and add it back to the "game.pak" file by using WinRar. When you start the game, select the easy difficulty setting and your units will be invincible.