Genesys Cloud allows users to modify custom script actions through the script editor interface. To edit actions, users navigate through Menu > Digital and Telephony > Interaction Assets > Scripts, select a specific script, and access the Actions list containing both custom and built-in options. The process involves clicking on the desired custom action name to view and modify its properties using the actions editor, followed by saving the changes. This functionality enables customization of interaction scripts within the platform's workflow management system.