The update_property_link function in Klaviyo is designed to replace existing values with new ones, preventing duplication or appending of values. Despite numerous attempts to append values, such as importing a CSV with the data type set to "list" or using personalization references, every effort results in replacing existing values instead of adding new ones. For instance, when attempting to append "blue" to an existing list like ["green"], the previous value is simply replaced, breaking the format. Even attempts to use code, like removing apostrophes or eliminating whitespace, fail to preserve the existing data, and the redirection leads to errors or broken pages. The issue persists regardless of method, leaving no viable solution for appending values.