Questions on Modem FW

[forfun]

I got a modem from swapmeet. When I checked (192.168.100.1), the FW is hacked FW with different MACID, S/N, from the label outside the box.

Now if I want to call TWC for internet and do not want to rent their modem (2.50/mo), but using the one I bought.

Will TWC automatic change the FW and correct the MACID, S/N that was labeled outside on the box to make it work?

Thanks!