Hello,

This is an update  Customizable Exp Modifier by  TBellovics  to version 1.31/32.

The BASE version
Found modified areas in the older Witcher source files (v1.11), copied just those modifications of the latest files (v1.31/32).

The Enhanced version
Everything in the base version.
Even with the modifications above, I found I was leveling too fast, so that on Death March!  difficulty, by the time I was very close to "meet with Ciri" which Quest suggests a level of 22, I was already at level 26, and there were several large Main-Line quest experience bumps soon to come.
I explored the mod Better Experience Curve - Feline - Griffin - Ursine - Wolf, however that mod changed the Experience Tables.  And would ONLY apply or work with a NEW GAME.   Also whatever rates I chose would apply throughout that game.
In a nutshell... Feline...Wolf  changed the number of exp points required to "reach the next level" - for every level in the game.

          Points needed to get to next level
Vanilla game:  Every level requires a FIXED amount to reach next level.  Levels  1->9  1000 exp    10->19 1500 exp    21->99  2000 exp
   or   1 1000  2 1000  3 1000....11 1500  12 1500...21 2000..25 2000...35 2000   and so on

Feline:  Every level requires 1010 more exp than previous level, in a mathematical progression which would level a player MUCH MUCH faster.
    or   1 1000  2 1010 3 1020 4  1030....11 1090 12 1100 12 1110...20 1180  51 1480 

Wolf:    Every level requires 1100 more exp than the previous level, in a mathematical progression which would make for SLOW level progression.
    or   1 1000  2 1100 3 1200 4  1300....11 1900 12 2000 12 2100... 31 4000  41 5000

I wanted to apply something like Wolf requirements, but which I could apply to saved games.

The solution - find where in the Witcher code where the  Rate Table rates are checked/used to see if a user has leveled up.
Fortunately all those checks are only done in one file.

• So I provide a SLIDER to choose "Use Exponential Leveling Table instead of Normal"
• Choosing a value of   5, would be the same as Feline.
• Choosing a value of   50, would be the same as Wolf.
• The effects of any change,  will show up in game, after:  Load game,  Gain Experience,  Save Game
  (this means, if you move the slider, and then choose character inventory,  the  experience bar  /  Points to next level, won't adjust until the above events.)

You Might get negative numbers:  When you look at your character inventory screen.   Here is an example.  
Level 30  [           ] -4750/2500
.
You are level 30.   With Vanilla you required 2000 points to go from level 30 to 31. 
You had already gotten 1000 points out of the 2000.
Then you used this Mod and changed the rate tables to a value of 25 (ursine).  So now instead of 2000 you require 2500 points to reach level 31.
Behind the scenes, your TOTAL experience (added together for each level all the way to 30)  was  46,000 points with Vanilla.
Now the TOTAL points to reach level 31 (with a table value of 25) is 51,750 - so you now need  51750 minus 46000 = 5750  to get from 30 to  31.  Your character screen will now show (after you save, or get exp)  -4750/2500   (5750 - 1000 you already had after reaching 30).


If you have the GOTY version or the version 1.32, it would probably be best if you installed the
----------------------------------
Installation:

• Unification patch for 1.32 - 1.31 - 1.31GOTY
• Perhaps Install the Custom Localization Fix mod by uacvax.
• Use "The Witcher 3 Mod Manager" to install the downloaded MOD.  It will place the Menu (XML) file and put it into the Bin folder automatically.
  

 
This mod allows you to modify the Vanilla XP modifier calculation for Quest rewards and from v2.1 you can alter enemy kills too.
(I know there is a lot of mods like this, but there is some more later :) )

There is an In Game Menu - Where you can modify variables for the following multipliers:
(the Vanilla value can also be chosen)

• Grey Quest modifier
• Level diff limit for grey quests
• Finished main game exp modifier
• Exp modifier if the calculated modifier is 0
• Exp modifier for Easy/Normal difficulty
• Exp modifier for Hard difficulty
• Exp modifier for Hardcore difficulty
• Level difference based Exp modifier for EP1
• Experience modifier maximum for EP1
  

So you can modify all the possible values of the XP modifier calculation for the vanilla system.

You can also enable or disable the XP reward modification for Enemy kills

• Unique slider for all difficulties
  

This mod is add a new XP modifier calculation system for the game, called Bonus/Malus system.
You can set a customizable threshold around the quest level:

• If Geralt's level is in the threshold: he gets the normal EXP for the quest
• If quest level is above Geralt+Threshold: Geralt will receive addition to
  exp modifier for every level (the percentage of the addition is
  customizable also the maximum of the modifier)
• If quest level is below Geralt-Threshold: Geralt will receive a reduction
  to exp modifier for every level (the percentage of the reduction is
  customizable also the minimum of the modifier)

All the above calculation is also affected by the difficulty modifier and the finished game modifier

Compatibility:
The mod is based on the v1.31/.32 version of the below scripts:

• r4Game.ws
• npc.ws
  

If you are using mods that alters those files you have to merge them: look for Script Merger by AnotherSymbiote on Nexus.