Set armor (demo version)
Use Notepad to edit "ScriptsDefaultGamerules.lua" file. Find the line with "armor = 0;" string and change the value to 255. Save the changes and run the game. You should always backup any files you change in case you make a mistake or it mucks up your game.
Invincibility (demo version)
Use Notepad to edit "ScriptsDefaultGamerules.lua". You should always backup any files you change in case you make a mistake or it mucks up your game. Find the following line:
ai_to_player_damage = { 1, 1, 1, 0.5, 0.5, 0.5 }
and change it to:
ai_to_player_damage = { 0, 0, 0, 0, 0, 0 }
Save the changes, and run the game.
Unlimited ammo (demo version)
Use Notepad to edit "ScriptsDefaultEntitiesWeapons.lua" file. You should always backup any files you change in case you make a mistake or it mucks up your game. Find the line with "loacal unlimitedAmmo = 0;" string and change the value to 1. Save the changes and run the game.