Well, when you kill a zombie - an "Exp" figure, (example "400", or "750") pops up at the bottom-right corner of your screen - right? That figure comes from the "entityclasses.xml" file, which is where all of the default Player and Zombie properties are defined, and you will find it under <entity_class name="zombieTemplateMale">, the actual Experience value defined here: <property name="ExperienceGain" value="400"/>. The "400" is the number of experience points which your character will receive, so that you can gain a Skill Point and thereby be able to advance in the game. I would not advise changing that line, as it could have a drastic impact on your game. However - if you want a few Dukes as well - note that under that line is "<property name="LootDropProb" value=".02"/> (Whether it drops a loot bag on death or not.) .
Modding the Loot Bag system is a bit complicated, so an easier way is by simply making the Dukes part of zombies "Harvest" - just chop up the carcass and get some bone, Dukes and whatever else you "need" manually. You could easily make a mod or add one, like the lines below - and add it to an existing entityclasses.xml mod. The Harvesting lines below, are all you need. Change them as you wish:
/Mods/MyMod/Config/entityclasses.xml
<configs>
<append xpath="/entity_classes/entity_class[contains(@name, 'zombie')]">
<drop event="Harvest" name="foodRottingFlesh" tag="butcherHarvest" count="8"/>
<drop event="Harvest" name="resourceAnimalFat" tag="butcherHarvest" count="3"/>
<drop event="Harvest" name="casinoCoin" tag="butcherHarvest" count="200"/> <---------------- This one will drop your Dukes. . . . .
<drop event="Harvest" name="resourceBone" tag="butcherHarvest" count="5"/>
<drop event="Harvest" name="resourceBone" tag="allToolsHarvest" count="2"/>
</append>
</configs>
To use the Loot Bag method:-
entityclasses.xml and the loot.xml
You could look at the <property name="LootDropProb" value=".02"/> as this will indicate whether it drops the yellow loot bag on death or not, and then note the <property name="LootDropEntityClass" value="EntityLootContainerRegular"/> below that line. It points to the EntityLootContainerRegular line in the Loot.xml, and from there - the lootgroup(s) that might be dropped. You could do what you want by adding the Dukes into those lootlists, instead of the Harvest method above - but it's quit a bit more work and testing..
Just some suggestions.... others will have perhaps better ideas?
pj