After bricking one router i decided not to try to increase the storage and go with the capabilities which it already have.
TL-MR3020 from TP-LINK have a UART but the problem with interconnection was TL-MR3020 out puts 3.3v and Arduino UNO is 5v. So after trying couple for methods trying to level the serial data voltage, finally 74LS04 is used the step up the TX from router to 5v and it was success and Arduino see the data.
Then tried to run a shell script from a webpage run in web server inside the router.
Anyways it works perfectly and more mods will be done soon.