Changes the law regarding political party primary elections

HB 1128 modifies Missouri's primary election rules by requiring voters to be registered with a political party as of the 23rd Tuesday before a primary election to vote in that party's primary. It updates voter data handling, allowing election authorities to provide limited registration information (including names, addresses, and party affiliation) to candidates and political parties for a fee, while restricting public internet access and commercial use. The bill also adds privacy protections for vulnerable voters, such as undercover law enforcement officers and domestic violence victims, by enabling them to close their residential addresses on voter records to prevent safety risks. Additionally, it specifies that written changes to party affiliation must be submitted in advance, with changes made within 23 weeks of a primary not taking effect until after the election.