Just dumped a Arris TG862A, what next?

Hi there! I'm very new to cable modem hacking. I just made a dump of the SPI flash inside a TG862A. Using binwalk and the firmware-mod-kit, I managed to extract the two filesystems. I also tried to modify /etc/passwd and point the root shell to /bin/sh, but of course it didn't work...
What's the next step? I got the full image, should I upload it somewhere?
Cheers

Ciaby