SDCL § 12-4-15: Voter information and party affiliation--Designation or change.

A person may designate or change that person's party affiliation, name, address, phone number, or email address by completing a new registration card. If a person completes a registration card to change that person's name, address, phone number, or email address, and leaves the field for party affiliation blank, the county auditor must list the person's party affiliation as the most recent party affiliation registered for that person. If a person completes a registration card to register to vote for the first time in the state and leaves the field for party affiliation blank, the county auditor must register that person's party affiliation as no party affiliation.