Updated for 3.0
Let me know if they're are any bugs or issues. If you play with the mod active while not playing a Morathi campaign, could you check on AI Morathi and see if she is applying the Mark of Slaanesh to units.

Compatibility with Variant Selector by Marthenil added:
https://steamcommunity.com/sharedfiles/filedetails/?id=2888171970

Sorceress of Slaanesh hero rebuilt, will now work with the correct model.
Supreme Sorceress of Slaanesh lord portrait scaling fixed.
Keeper of Secrets bound spells can now be enabled through different skills and technologies.

Bugfix. Hero quick recruit table used for testing removed from pack.

Rewrote the .bin file and some other small housekeeping updates. Everything seems to be working. No Isabella or experience problems with other factions.

wh_campaign_experience_triggers.lua updated.

Sisters of Slaughter now able to receive the Mark of Slaanesh.

Relations with Azazel and Sigvald now start at a base of 0, the same as other Slaaneshi factions.

Diplomacy changes, Morathi will now start with:

• +10 relations with Malekith (up from vanilla -10), and can further increase relations by +20 (to a total of +30) with the 'Absolute Devotion' character skill.
  
• +30 relations with Ghrond (up from vanilla -10), and can further increase relations by +20 (to a total of +50) with the 'First Sorceress' character skill.
  
• -40 relations with Hellebron (down from vanilla -10), and can further decrease relations by -10 (to a total of -50) with the 'Rituals of Blood' character skill.
  
• -10 relations with all Beastman factions (up from vanilla -40), normalising relations to the same base level as other Chaos-aligned factions for the Chaos-aligned Morathi.
  
• 0 relations with all Norscan factions (up from vanilla -10).

Morathi's 'Grotesque Sacrifices' character skill will now give:

• +30 relations with Norscan factions, as in vanilla.
  
• +30 relations with Slaaneshi factions, including Azazel and Sigvald.
  
• -30 relations with Khornate factions, including Valkia and Taurox.
  
• +10 with all other Warriors of Chaos, Daemons of Chaos, and Beastman factions, increasing them to a base of 0.

Dark Elf Master hero can now take the special Slaanesh skill line.

Slaaneshi Witch Elves passive hex ability 'Rapture of Slaanesh' toned down to a max of -8 MD, in line with the Glamour of Slaanesh (-5 MD) and Allure of Slaanesh (-8 MD) character skills, but will max out slightly earlier at 120 kills.

Chaos (Norscan) War Hounds added to the special Norscan recruitment defensive building, the Garden of Sensual Delights (Norscan Outpost), that is able to be built only in Norscan provinces.