Before You start with this one keep in mind You'll be changing a file so make a backup copy before Youi begin. Now, use Notepad to edit "default.ini" file (make a backup first!). Scroll down to the [Difficulty] section and change the values of the following variables:
AI visual acuity multiplier - How well AIs can see
AI auditory acuity multiplier - How well AIs can hear
AI tactile acuity multiplier - How well AIs can feel
AI hitpoints multiplier - All AI starting hitpoints will be scaled by this
AI-to-player damage multiplier - All damage applied to the player by the AI is scaled by this
For example, set them to 0 (zero) and enemies won't be able to see you, hear you and even hurt you.
Disable loadscreen tips and loadscreen flavor text
Again make a backup coipy before You proceede with this. Use Notepad to open 'HelpText.sch' file located in the Thief 3\Content\T3\Books\English folder (make a backup first!). Select all the text, delete it, and then save the changes. This will loadscreen tips.
To disable flavor text that appears on the loading screens, you need to open 'Quotes.sch' file located in the Thief 3\Content\T3\Books\English\String_Tags folder using Notepad (make a backup first!). Now you need to replace each quote with a " " (a space; do not leave an empty string, or you'll get a message about having no messages to display). Save the changes. Note that removing these quotes may cause you to miss out on certain details of the story, so keep this in mind.
Disable First-Person Head Bobbing
To disable the up-and-down bobbing motion of the camera use Notepad to edit file "T3PlayerAnims.ini" (make a backup first!). In the "-- NORMAL GROUND MOVEMENT --" section change all [Forward1] through [Forward6] from 'Translate=false' to 'Translate=true'.
Metal Age Nightvision
Although shadows are important to hide Garrett, sometimes it can too dark to see while hiding. Crank up the Gamma/Brightness correction in your options menu to see the surroundings while remaining hidden.
Don't Leave Angry
Since the stages are often divided up into separate maps, you find yourself transitioning from one part to the other. If you are being chased by a guard, never leave the map and come back expecting everything to be normal. The guard chasing you will still be there and alerted to your presence. Always make an effort to hide in the same map you are to avoid forgetting that a guard (or party of guards) are waiting for you on the next map.
The map transitions are a good place to hide (they are almost always completely dark). Simply go into the map transition and decline to go into the next section. Garrett will stay in the murky, smoky portal and almost always out of the way of all patrols.
Free Water Arrows
You can get free water arrows in the training mission (which carries over to your subsequent missions) by waiting by the douse the torch exercise for water crystals to keep respawning. Before you leave the Blue Heron Inn forever, you may want to take your fill of 25 water arrows, which will go a long way in helping you keep shopping costs down.
By day 3 (after meeting with the Keepers the first time), players may choose to ally with the Hammerites, the Pagans, or both by doing them small favours. Allies are helpful since they will not attack you, and allow you to hide in their turf when you flee the City Watch (who you may never ally with).
Befriend the Hammerites by locating and destroying the large cockroaches that inhabit the city. For each one you destroy, you increase Hammerite friendliness by one point. You also befriend Hammerites by destroying any undead using Holy Water or Fire Arrows. This may take a little while, but the beetles are easy to find. Undead are even easier to find, but you may need to stock up on fire arrows to deal with them adequately.
Befriend the Pagans by locating green stones with the mark of the Trickster or by locating the elemental archway in the Pagan turf and firing a moss arrow into the target. The green stones are harder to find early in the game, so the elemental arch is a much better choice to befriend the Pagans. Simply shoot any one of the four purple nodes on the arch with an elemental arrow. Consider using moss arrows for this purpose; you can fire as many elemental arrows into the Pagans' elemental arch as you can afford to immediately ally them with you when the opportunity arises.
Moss arrows are more plentiful as you pick up many in the city; more if you don't use them. You can save your fire, gas, and water arrows for your missions.
Killing, blackjacking, or looting from the Hammerites or Pagans will decrease your standing with that faction.