Does such a mod exist?
http://fallout3nexus.com/downloads/file.php?id=7636 triples the sneak critical damage from vanilla Knives, Combat Knives, Switchblades, Rippers and the unique and follower variants, and adds 50% to all other Melee and Unarmed sneak attacks. It's not an immediate sneak kill, but it's actually a bit unrealistic and overpowered to kill silently with one stab. You use a garrotte for that. LFox made a http://www.fallout3nexus.com/downloads/file.php?id=7208 perk that lets you insta-kill anyone as long as you have the 100 Sneak and 7 Ag required to take it.
http://fallout3nexus.com/downloads/file.php?id=712 and http://www.fallout3nexus.com/downloads/file.php?id=1625 allow you to rebuild fallen robots and build new ones respectively, which is mainly to allow high science and repair to help in combat with a little investment, and there's a http://www.fallout3nexus.com/downloads/file.php?id=3097 to balance using both together.
My http://fallout3nexus.com/downloads/file.php?id=7886 mod lets you salvage Scrap Metal, possibly a Fission Battery and varying amounts of new items for Cyborgs. However, two of those items are highly poisonous, so a sufficiently stealthy character could, in theory, reverse pickpocket them onto enemies or simply dump them in an eating area. However, this is not a viable strategy in most cases since not many hostiles actually have eating enabled in their AI, and many people only eat at specific times of day and waiting for that time can be glitchy, they may decide they're not hungry. There's an Energy Cell adapter included, too, but the results are designed to have equivalent value, it's only for Cyborgs and it doesn't actually check Science and Repair.
LFox made a bunch of http://www.fallout3nexus.com/downloads/file.php?id=5272 which may suit a more peaceful character better than lethal weapons.