If you're using this mod, you need to put it AFTER the submod in the load order through the mod manager.

The reason is that the mod already includes a TTC script, but it makes the Warriors core. In order for the submod to take effect and make them special (I followed 6ed rules, in which mortals for demon armies count as special units) it needs to override that script. In order for that override to work, you have to put the Nurgle Warriors after the submod in the load order.

It's up to you, of course, to decide what rules you prefer. :)