ensuring voices don't disappear + extending?

I'm intrigued by this service, but out of curiosity, can users remove voices from the Voice Universe that you might be currently using? And if not, what if I attempt to build a voice and it turns out horribly and *I* want to remove it?

Secondary question, what if you find a voice that you think is really pretty good, like a celebrity, but you think it could be better if you fed in more voice data? Can you somehow copy and extend an existing voice?