How easy / difficult is the spell to put down the undead without harming or destroying the corpse?

Would being under the influence of Koth make it more difficult for Kell to cast this spell?

Since I want him being hit with affliction of plants and small animals dying around him and giving people visions of their deaths. How would people of Nott react to him trying to help with the undead, while it kind of looks like he's spreading the rot himself given that living things keep dying in his presence?