I think that in this fic Buffy is still with Riley when something happens and she transforms into a boy.Thanks for any help.

there's a fic called impossibly delightful flesh that has most of the scoobies, including buffy switching genders. i've got a copy saved if you want it. menolly_23@yahoo.com

Impossibly Delightful Flesh by Sadbhyl is over at sinister attractions.

http://www.sinister-attraction.net/stories/s/impossiblydelightful.htm

Summary: The Scoobies have an accident that has them questioning the deeper issues of sexuality, gender, and the heart.

Its not it because in my fic spike is a boy.

Sorry i meant man!

i don't know if this is it oir not. it's season 6 and buffy comes back from the dead as a man
Carpe Frenulum by sabershadowkat
http://www.sabershadowkat.com/buffy/carpefrenulum.html

Thank you but that's not it because there's no Riley.