I've found some choice story chapters in bearchive.com and cyoc.net. Just thought I might share:
Debbie becomes a black girl...:
http://www.bearchive.com/~addventure.../008/8071.html
...and again...:
http://www.bearchive.com/~addventure...44/344335.html
...and again.:
http://www.bearchive.com/~addventure...019/19837.html
Nikki to Niquita... (Latina transformation):
http://www.bearchive.com/~addventure.../008/8072.html
And apparently, it's a recurring change:
http://www.bearchive.com/~addventure...28/428792.html
Whitebread Caucasian girl into voluptuous Asian:
http://www.cyoc.net/stories/chapter_...apter_id=27308
Four Giggling Girls story branch; fat AND black (read on; they turn hot at the end):
http://www.cyoc.net/stories/chapter_...hapter_id=9224
Crystal becomes a black woman:
http://www.cyoc.net/stories/chapter_...apter_id=35775
Models undergo a race transformation to appease their boss:
http://www.cyoc.net/stories/chapter_...apter_id=15385
Naoko decides whether to go partial or full:
http://www.bearchive.com/~addventure...24/424857.html
Amber changes into an African Amazon (don't ask me...):
http://www.bearchive.com/~addventure...51/351056.html