They don't have a "cancel ballot" button. When you fill out and print the new online ballot it will cancel any previously sent ballots. They site says "Caution: If you continue, a ballot previously mailed to you will be canceled"

They don't.

Wow. This post was dangerous disinformation. I have independently confirmed this is false and ballots cannot be canceled or changed.

It is indeed possible to see addresses where ballots were mailed, and I was able to view a politician’s information using only their name and date of birth gleaned from Wikipedia.

I’m sure this information can be found in any number of ways, however. There is also a disclaimer stating “ If your information is confidential or you are not yet 18 years old, contact your county elections official to confirm your registration status.” which indicates using that site to register has no implication of privacy.