If you have a more powerful standalone router, you might want to use the HG658 v2 purely as a modem (Bridge Mode). Some ISP firmware makes this difficult to configure properly. Custom firmware often provides a cleaner Bridge Mode implementation, passing the public IP directly to your superior router.
If you are looking to modify the device's behavior, here are the most viable paths: 1. Advanced Configuration (Non-Destructive) huawei hg658 v2 custom firmware