@SimonC, I don't believe you can edit a sourced list. From NetSuite Help "Important After you create a select or multi-select field that is sourced from a record or list, you cannot add additional values with Field.addSelectOption(options). The select values are determined by the source record or list." You could pull the list though and generate a select using ".addSelectOption" method to build a select field from scratch. https://system.netsuite.com/app/help/helpcenter.nl?fid=section_4449822161.html