once a character is created and you've started adventuring, is there a way to change his/her personality? i've got one character whose voice i've gotten sick of and want to change it.

You can change voice, portrait, and personality (and your name too, I think). Right Click the character to get to the char screen. Right below their portrait, you'll notice that you can click on their name. Click (or was it right-click?) their name and it will take you back to the character personality screen.