We use Xilinx Zynq ZC702 platform with FreeRTOS+TCP for our applications. I have a requirement of upgrading the “Network Interface Port Layer” as defined in to support two interfaces, one whereby packets are sent via ethernet interface of Xilinx Zynq ZC702 and other via our custom applications. Is this possible by just modifying the Network interface port layer or other modifications are also required? Kindly clarify?

Without a deeper understanding of what it is you are trying to do it is difficult to say for sure. We do however have an experimental version of FreeRTOS+TCP that supports multiple interfaces (with different IP address, MAC addresses, etc.).