Romek... You do realize I can change anything about a unit in object editor?
The original lore around the warlock was they would destroy there enemies utterly from the inside, raise the dead, summon demons. All Demonic power, infact they created the first death knights.
So Warlocks can summon demons and raise dead. If you guys want I can take away the ability with raise dead. Or I can make a spell that summons a imp or something.
If you could give more details it would make it easier.. A tanker doesnt mean much.