Custom game
Use a text editor such as notepad to edit the "difficulty.cfg" file in the "\Velvet Assassin\aio\" directory. Edit the various files as desired to change the game. For example, change the "NPCDamage = 1" to "NPCDamage = 0". You can also change the values in the "weapons.cfg" file in the same directory to adjust the weapons.
Enemies cannot see Violet
Use a text editor such as notepad to edit the enemy files in the "\Velvet Assassin\aio\enemyclasses" directory. Set all the FOV values to 0, and enemies will be blind to Violet. She will only be detected if you bump into them.