My version never had SSE branding. It is stock, as far as I can tell. The only thing they added was the SSE login details (username). I currently use a ZyXel VMG8324 so haven't used the Technicolor for a while now.
I did manage to gain access to the device using SSH using the account 'tech'. The password is printed on the bottom of the device, in the 'Access Key' section. See if SSH is enabled on your device. But no matter what I did, I couldn't get telnet working. Having said that, my OpenWrt knowledge is pretty rudimentary. All configuration is done using the
UCI System, which is easy(ish) to learn.
Not all commands are allowed for user 'tech', even the ones they claim are allowed. It is a restrictive interface and I couldn't figure out how to drop into a full shell.
The branding could be more tricky to remove without having access to vanilla firmware.