You can use Cy_BLE_GAPP_UpdateAdvScanData() during advertising is on. Before calling this function, you need do below steps:
1)define the data array of new advertising packet by yourself -- advdata. You can get the array in BLE_config.c (-- cy_ble_discoveryData), by setting in BLE customizer accordingly.
2)pass the array address to target struct to be configured:
cy_ble_configPtr- >discoveryModeInfo[CY_BLE_PERIPHERAL_CONFIGURATION_0_INDEX].advData = &advdata