This mod changes the XP for kills based on the difficulty you are playing on so it works similar to Fallout 3's Mechanic. In Fallout 4 there is no difference in XP between any of the difficulties. So all difficulty modifiers are set to 1 (100%) in Vanilla Fallout 4. This mod does not change xp for other factors such as quests or map marker finding as the difficulty does not modify the difficulty of the quest itself so should not be changed.

In my opinion playing on higher difficulties isn't rewarding enough and you should be granted additional XP. Or if you are completely crazy and want a real challenge i have decided to create an "inverse" option which makes XP more scarce the higher the difficulty.

Here are the XP multipliers for each difficulty:

DifficultyXPScaling.esp
Very Easy - 0.6 (60% of Original)
Easy - 0.8 (80% of Original)
Normal - 1.0 (100% of Original)
Hard - 1.2 (120% of Original)
Very Hard - 1.4 (140% of Original)
Survival - 1.65 (165% of Original)

Here are the values for the inverse modification.

InverseDifficultyXPScaling.esp
Very Easy - 1.4 (140% of Original)
Easy - 1.2 (120% of Original)
Normal - 1.0 (100% of Original)
Hard - 0.8 (80% of Original)
Very Hard - 0.6 (60% of Original)
Survival - 0.35 (35% of Original)

There are also other options:

DifficultyXPScaling2.esp
Very Easy - 0.75 (75% of Original)
Easy - 0.875 (87.5% of Original)
Normal - 1.0 (100% of Original)
Hard - 1.125 (112.5% of Original)
Very Hard - 1.25 (125% of Original)
Survival - 1.4 (140% of Original)

DifficultyXPScaling3.esp
Very Easy - 0.7 (70% of Original)
Easy - 0.85 (85% of Original)
Normal - 1.0 (100% of Original)
Hard - 1.15 (115% of Original)
Very Hard - 1.30 (130% of Original)
Survival - 1.5(150% of Original)

5x XP for Kills.esp
Gives you 5x XP for kills on all difficulties (500% of original)

To install place the DifficultyXPScaling.esp/InverseXPScaling.esp file in your ...Fallout 4/Data Folder.

Please note you will have to enable modding for this game if you haven't already to do this:

Navigate to your Documents/My Games/Fallout4 Folder.

You will need to add the following line to the Fallout4Prefs.ini file below the section marked [Launcher]:

bEnableFileSelection=1

You will need to change the following line in Fallout4.ini:

sResourceDataDirsFinal=STRINGS\, TEXTURES\, MUSIC\, SOUND\, INTERFACE\, MESHES\, PROGRAMS\, MATERIALS\, LODSETTINGS\, VIS\, MISC\, SCRIPTS\, SHADERSFX\