User blog comment:Miskos3/Fairy Tail Chapter 486: The Fourth Guest, Review/@comment-6401212-20160524052444/@comment-7418318-20160524130450

Could be. As I said we know that Zeref did all of that, including modifying Humans, so it's entirely possible.

The only thing we have no confirmation of Zeref doing is using a disembodied soul as the basis for a new being... but I wouldn't be surprised if he could (or actually did) do that too.