User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-24098614-20150802064153/@comment-26668768-20150802214921

Yup like striker said.....akeno or rias can change said body part back to normal by sucking the energy out.

He will prolly learn to change back himself after he has the new body a bit longer but really would you want to learn to do it yourself if the way above was the only other way.