Change message Your username already exists.

Hello, I am using MB User profile and when the user try to register with user/email that exist so I am getting the next message

"Your username already exists." or "Your email already exists."

My questions are:

1. Is possible change this messages?
2. The fields are blank so the user should fill again all fields to try other username o email. So is possible taht fields are fill with the initial data? can you understand me?

Thank you in advanced