This mod reduces warmongering penalties by default, halving them for earlier eras and leveling off at 24 instead of 32 in the modern eras. Additionally, Joint Wars provide 50% warmongering penalties instead of the full 100%.
The xml file is annotated so that it is easily customizable. Simply change the numerical values to whatever reasonable value you wish (extreme values will probably break your game somehow).
In order to edit the warmonger values navigate to Documents\My Games\Sid Meier's Civilization VI\Mods\TCS Customizable Warmonger Penalties and open the TCS_Improved_Warmongering.xml file with any text editor, although I strongly recommend Notepad++.
Unzip to your Documents\My Games\Sid Meier's Civilization VI\Mods directory.
Customizable Warmonger Penalties 1.1
This mod reduces warmongering penalties by default and makes it easy for you to customize the values