in your case Charter is THE MAN.
Your TOS governs what you can and cannot do, and what THE MAN can do.
They can raise your rates, and not give you any change in service.
You make any changes and get caught, you lose.
Some companies allow for a small fee, the residential customer to get a static IP and setup FTP, HTTP and SMTP services, some do not and require a business class account.
Other ISP's will not allow e-mail from a server that is sending from a particular block of IP addresses that have been designated as residential accounts.
That said, in the past I had a forum and e-mail server set up on a ComCast residential account and had e-mails bounced many times due to the originating IP address.
It was low key but I got tired of the risk involved and decided it really was not worth it.
If they want more than just a small fee, you could find a host that will host your domain for FTP and e-mail for a small fee.