Answer
Rather than attempting the update directly inside the insert-triggered event (which risks a mutating-table error), trigger a background job instead: build an attribute string with the relevant key/field values from the record (using Client_SYS.Add_To_Attr), then call Transaction_SYS.Deferred_Call, passing a custom procedure name, the attribute string, and a description — the deferred call runs as a separate background job after the main insert transaction has fully completed, avoiding the mutating-table conflict entirely while still letting the custom procedure read and update the just-inserted record's other fields.