I have found out a way to bypass that. It has worked for nokia 2425g router
What i am doing is, taking that backup configuration file, then decrypting it. this way that configuration can be reverse engineered. All the values are stored in a xml file including wifi password.
with that, i was able to enable telnet in the router, also i was able to change all of the greyed out settings. I had changed the channel, enabled telnet, Also there is the option to remove tr069 client, as that is what used by airtel to change the settings from there side. I was also able to enable both ipv4 and ipv6 in the wan settings, but since that needs to be configured from back, it couldnt work.
Also got some interesting information like the chip used is MTK7528 about which i am not able to find any datasheet online.
I am not mentioning the exact guideline here now, but maybe do in some time. Also, It can be very dangerous as if any wrong value is changed, there is a high probability the device may brick.
And one more thing, any idea what enabling the IPTV option does? like, airtel didnt mention about any such service for tv etc, xstream box uses dish for live tv instead of net.