VTAM® uses USS tables to define messages and certain operator commands. If you want to change the text or other characteristics of a message or change the syntax or default values for a command, you can do so by creating a supplementary USS table. Only the commands and messages that you want to change need to be defined in the supplementary USS table.
See Unformatted system services tables for information on the macroinstructions that define a USS table. See z/OS Communications Server: SNA Network Implementation Guide for information about how the table is used.