INI file

The 2 INI files the game uses are Fallout.ini and FalloutPrefs.ini. If these are not present in Documents\My Games\FalloutNV they will be generated and populated by FalloutNVLauncher.exe upon launch.

Types of properties used
All properties start with a letter indicating the type of value you can enter as valid.

FalloutCustom.ini
If the user has the JIP LN NVSE Plugin installed, the game will be able to read a third INI file in the same location as the others, named FalloutCustom.ini, akin to the same type of INI present in Fallout 4 and Skyrim.

This type of INI is supposed to be populated by the user with pre-existing properties from the other 2 INI's and with values of their choosing, these will take priority over the original properties and allow INI editing while keeping defaults intact.

Example of how FalloutCustom is used: