I would like to know if there is a way for me to change a router's default settings. When I say that I don't mean logging in the page setup and configuring it. What I mean is to change the settings that the router will be after you reset it (Even if it means brute-forcing my way there).
The factory settings are stored in the firmware. So you have to flash the router with a custom firmware.
But first, you have to find where those settings are into the firmware.
In short: you can't, except if you have lots of free time