What is this mod?
Adds a passive toggle to enable/disable the Half-Illithid visuals (veins, eyes, etc) which can be turned on/off at will on a per character basis.
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Adds a passive toggle to enable/disable the Half-Illithid visuals and adds 3 abilities to adjust intensity of Vein Depth, intensity of Vein Color, or Eye Effect On/Off.

Why develop this mod?
After a certain action in Act 3 (which I'm assuming you know about if you are reading this; otherwise spoilers for Act 3), your character's visuals are altered.  I did not like the effect and wanted my character back to the way they looked.  There are numerous mods on Nexus that claim to accomplish this via different methods.  Most of the texture replacement ones had issues.  But here are a few of the notable alternatives:

• Hide Half-Illithid Visuals (maedhros1) - Modifies the Material Override to remove effects from the override.  Has an option to leave veins and remove only the effect on the eyes.
• Permanently Remove Partial-Illithid (Astral Tadpole) Appearance (refinedocelot) - Less a mod and more instructions for how to use SE console to remove the effect from a character or party member.  Instructions to remove the 'buff' which causes the effect instead of the effect itself.  Could cause problems if Larian ties any conditions to having that 'buff'.  This one somewhat inspired me to make a toggleable passive.
• klementineQt commented in multiple texture replacers - Gave instructions for removing the Material Override effect from the character.  This is the method used by this mod.
  

How Does the Mod Work (Toggle)
A ScriptExtender script checks statuses as they are added to the character.  If the character has the Half-Illithid 'buff' but not the toggle ability, the toggle ability is added.  When the toggle is used, it adds a hidden buff for either ON or OFF and the ScriptExtender script runs the command to remove or add the Material Override from that character.

Can be installed before or after the Act 3 event.  If installed after, you just need to apply any status to the character to get the toggle to show up.  Cast any buff on them should work.

How Does the Mod Work (Config)
Adds the Toggle from above as well as 3 abilities to set Vein Depth (0ff, 25%, 50%, 75%, Full), Vein Color Strength (Off, 25%, 50%, 75%, Full) and Eye Effect On/Off.  Each will add a hidden boost for the selected configuration option.  If the Toggle is on, it will show whatever you have selected.  If Toggle is off, it hides all effects regardless of chosen setting.  If you Toggle back on, it show whatever configuration you have set.  Changing settings while Toggled off will set the setting, but not show effect until next time Toggled back on.

As with above, can be installed any time.  If you are upgrading from the Toggle version, simply toggle the ability once to get the new Config options to show up.  Once you have set the options, you can remove the skills from your hotbar.  They will be on your Common tab in your Spellbook if you want to change them again.

Note About the Half-Illithid Effect
This following section is a little bit technical, but is important to understand regarding what can and cannot be accomplished.

• The Half-Illithid Effect is handled by the game via something called a CustomMaterialOverride.
• These are defined in the game files as ScriptMaterialOverride.
• The ScriptMaterialOverride for Half-Illithid Effect uses the Scar element and Eyes element.
• The Scar element has 3 parameters to tinker with: Scar_Weight, IllithidColorWeight, ScarIndex.
• After tinkering with ScarIndex, I could get it to use the other available scars, but based on the ones from CC, none seemed appropriate so I ignored changing this parameter.
• For every option I provided, I had to make a number of elements: ScriptMaterialOverridePreset, Config Spell, Config Effect, and then modify the code of the script to account for every option.  Therefore I will not entertain requests to make more options.
• For both Vein Depth and Vein Color Strength the 25% setting is almost indistinguishable from Off.
  

Compatibility
Should be compatible with everything.  The ScriptExtender script and ability are new objects so there is nothing to conflict.
Can even be used alongside Hide Half-Illithid Visuals Eyes Only version if you want to always hide the eyes effect but toggle the veins on/off via the toggle ability from this mod.

Requirements

• BG3SE (ScriptExtender) - Recommended to install this via BG3MM
  

Installation
Files are package as .pak file and ready for use by a mod manager.  Recommended to install via BG3 Mod Manager.

My Other Mods:

• Valdacil's Spell Adjustments - Started out to align Vanilla and 5E Spells duration and concentration with Larian philosophy.  Developed into various tweaks for improved gameplay and make some less used spells more interesting.
• Valdacil's Half-Illithid Effect Toggle - Toggle ability to hide visuals from a certain Act 3 event on a per character basis.  Also has a configurable option.
• Basic Actions Consolidated - Adds a hotbar icon to contain the Basic Actions to free up hotbar space
• Spore Druid Extra Attack - Adds Extra Attack to Spore Druid since Spore is a martial focused subclass and Moon gets Extra Attack while wildshaped.
• Amulet of Rituals Additional Instruments - Adds missing instruments to the Amulet of Rituals mod
• JWL Scratch is Back Val Tweaks - Various tweaks to the excellent JWL Scratch is Back to give our Best Boy more balance across the various forms.
  

Credits

• klementineQT - For the comment in multiple mods with instructions for the Osi.RemoveCustomMaterialOverride method used by this mod
• maedhros1 - For their mod which accomplishes something similar in a different way.
• refinedocelot - For their instructions and comments in their mod which inspired me to take the concept from klementineQT and turn it into a toggleable passive
• Norbyte - For their modding tools, especially BG3SE