User blog comment:FairyRaven/Fairy Tail Chapter 368: The Third Seal, Review and Commentary/@comment-82.20.156.238-20140128065458/@comment-24066070-20140128211442

I wonder if those turned into a demon will still look exactly like before when they assume their human form.

If they can, they can just return to their guild without being found out and launch a surprise attack by suddenly revealing what happened to them.