Is This a Zombie? Novels
 

http://myanimelist.net/anime/8841/Ko...Zombie_Desu_ka
https://www.youtube.com/watch?v=fllrvN-OAnw Anime opening

Aikawa Ayumu will fight a enemy cross dressing in a Mahou Shoujo outfit(albeit very reluctantly) if his zombie abilities are insufficient for the task.

In Kore wa Zombie Desu ka? novels 11 and 12 Ayumu is turned into a girl after his male friend Orito gets his wish magically granted. I don't know what he does to change back.

Volume 11
http://i.imgur.com/FI4pBaw.jpg
http://i.imgur.com/04aNApD.jpg
http://i.imgur.com/toWhm4c.jpg

Volume 12
http://i.imgur.com/gLIZMiq.jpg
http://i.imgur.com/mTxxRlx.jpg

The cover for volume 19 features female Ayumu in his Mahou Shoujo outfit. I don't know the details about volume 19 except that all of Ayumu's love interests have settled down with him and that the next volume will be the last.

Volume 19
http://i.imgur.com/f2t6NNw.jpg

http://i.imgur.com/SwpwSH1.jpg (Fan Art)

On a personal note I think Ayumu would prefer to be a girl when he is a Mahou Shoujo. It would certainly be less humiliating than wearing a Mahou Shoujo outfit as a guy.

Re: Is This a Zombie? Novels
 

I agree.

Re: Is This a Zombie? Novels
 

Not sure but I believe this extra came from one of the later volumes of the manga. Abit of a shame the translations are so far behind.

http://tieba.baidu.com/p/3158207893?lp=5028&mo_device=1 The chapter plot is reminiscent of the third anime OVA but instead of a invisibility potion its a gender change one.