This mod overhauls the Thief skills for Requiem - The Roleplaying Overhaul 5.4.0. The main idea is to make Thieves a viable playstyle throughout the game, by opening up new ways to deal with your problems, in combat and out, while at the same time slowing leveling to make becoming a Master Thief a real challenge, and fittingly rewarding.

Perks

In Requiem you have a limited number of perks, and this means you have to specialize to succeed. What this means in practice is that playing as a Thief, and spending about ten perks in Thief skills to do, so cripples your character. The usual way around this is to only take a single perk in each tree, then use enchantments to make up for it. To solve this, all non-combat Thief perks (Lockpicking/Pickpocketing and Speechcraft) are given for free once you have the correct skill level and have taken the first perk in the tree. This means you can play as a Thief without crippling your character. This can be toggled of in the MCM menu if you feel it is too powerful.

Sneak

Sneak attacks have been reworked almost entirely, to make playing an assassin a more reasonable playstyle. Undead and Dwemer can be sneak attacked with the right perks and weapons, and the sneak attack multiplier is much more dynamic.

• Now characters that haven't taken the first sneak perk cannot sneak attack at all, and their sneak exp won't rise until they take it. Taking the first perk gives you 2x sneak attacks.
• The second perk gives the usual 50% AP on sneak attacks, but also causes your sneak attack multiplier to rise with your sneak skill (not with bows). 2.5x at 25 and 5x at 50. This way you are always improving between perks. 
• The third perk allows sneak attacks against the Undead, as long as you are using a Silver or Daedric weapon. The sneak attack modifier now increase at a higher rate. 7.5x at 50 and 15x at 100, or 4x with bows.
• The forth perk allows sneak attacks against Dwemer, using any weapon. The sneak attack bonus is a flat 15x. With bows it scales up to 5x.
  

Sneak perks (left hand tree), now all give a 15% stealth bonus. Sneak II has been removed, and its effects spread around other perks. Muffled movement now actually muffles your movement.

Lockpicking

A new perk, Expert Lockpicking has been added, meaning that your Lockpicking Expertise ends the game higher. Each perk has also been given a secondary effect.

• Advanced Lockpicking gives you a 50% chance to avoid detection when lockpicking.
• Sophisticated Lockpicking gives you a copy of the key for every lock you pick that has one.
• Expert Lockpicking gives you a 100% chance to avoid detection when lockpicking.
• Masterly Lockpicking means that picks never break.
  

Pickpocketing

In Vanilla Requiem Pickpocketing heavily incentivizes savescuming. Fortify Pickpocketing Enchantments also stack, allowing you to be a master pickpocket with only a one perk investment. This has been changed, hopefully to allow a pickpocket playthrough to feel natural. Enchantments no longer stack, so you have to invest to be a master pickpocket. The cap on pickpocketing chance has been lowered to 95%, so at any time you might fail, even as a master. This will rise by 1% for every main perk you take, up to 99% for a master. If you have completed the Thieves Guild Questline this is raised to 100, due to Nocturnals blessing. Skill gain has been halved, as before it was the easiest skill in the game to level. The ability to kill several enemy types by plucking their hearts out has been added, to give pickpocket some more utility.

• Cutpurse: Unlocks Pickpocketing. Gold always has a 95% chance of success. 
• Nimble Fingers: Pickpocket chance increases with half of your Pickpocket skill, up to a max of 50% extra chance. Keys, potions and scrolls always have a 96% chance of success.
• Fingersmith: Pickpocket chance increases with Pickpocket skill, up to a max of 100% extra chance. Allows reverse Pickpocketing poison's.
• Misdirection allow you to pickpocket the soul gems from Dwemer, and the Taproots from Spriggans, killing them instantly. The success chance is equal to your pickpocketing skill. Centurions and Enchanted Spheres are immune.
  

In addition, the below changes have been made.

• The petty crime threshold, where guards can be persuaded to ignore you has been raised to 300, so you have other options when you get caught apart from instantly going to jail or dying. This should prevent the need for savescuming.
• NPC's will no longer comment on you sneaking and pickpocketing, as I felt this was unrealistic, as you are supposed to be unseen while pickpocketing.
• All buffs to pickpocketing sleeping targets have been removed, as I felt this ruined the leveling curve, and it is a bit unrealistic.
• The leveling curve has been changed significantly, making high levels of pickpocketing much harder.
• Draugr can now be pickpocketed, allowing you to take the Dragonstone without fighting.
• You cannot pickpocket gold from trainers or from Guards that you have bribed.
  

Speechcraft

Speechcraft is a skill tree that most players take one skill then forget about, easily reaching 100 by mid game just by selling. Even if you don't take the perk, you still reach 100, there is basically no way to avoid it. The below changes make the skill harder to use, to put it on par with rest of the skills.

• Silver tongue is now the first speechcraft perk. Without it, the speechcraft skill can't be raised, intimidation checks are impossible, and only very easy speech checks can be done. 
• Haggling now requires Silver tongue and 25 speech skill.
  

These changes meant that you now need to invest a perk in speechcraft to use it, like all other skills.

Misc

• All shopkeeper inventory chests have been placed underground again, as even master lockpicking is far to easy to achieve, breaking the games economy.
• An option in the MCM menu lets you permanently set all misc crime stats to 0, for Lawful players who lost there blessing by mistake. Off by default.
  

Thank you Ogerboss and the Requiem Dungeon masters for Requiem.