It absolutely can be done remotely.
Every one of these modems does SNMP, exports everything it has in the way of statistics, and they can read it remotely
The modems are nowadays configured to only allow requests from certain ip space with certain passwords because you could actually accomplish a lot in the docsis 1.0 days by messing around with SNMP.
Depending on the modem manufacturer, you can still poison them with your own locally-loaded TFTP configuration file to override the speed configured from your cable provider.
Disclaimer: The FBI was cracking down on people who were doing this.
The modems are nowadays configured to only allow requests from certain ip space with certain passwords because you could actually accomplish a lot in the docsis 1.0 days by messing around with SNMP.