Unlike what some people may think, you can't actually modify your cable connection on most networks. Comcast uses an AT&T provisioning system to load a configuration file onto the modem during it's initialization cycle. This file is encrypted by the CMTS and sent to the modem based on it's MAC address. This file also determines the maximum speed the modem will operate at. It is determined by the account package and cannot be manually changed by anyone in local markets, it can only be manually changed by the AT&T Network Operations Center. Anyone who does not have a standard configuration file will be caught during a system audit, their account information polled, and the proper configuration file assigned. If the modem does not accept the config file, the account is blocked. You may wish to be very careful when trying to "hack" an HSD account otherwise you may have a nasty e-mail from the Abuse team in your Inbox.
Can anyone guess who I work for?