You can use the Microsoft PowerShell to open a serial port and send commands.
Or did you have that already ? Does it have to be using ethernet ?
Perhaps using wget for windows, and retrieve something like http: //192.168.0.100?AB01CC804010
The number after the '?' could be the hexadecimal value for the relays.
A better option is perhaps using the PowerShell to create a client and use Downloadfile: Native alternative to wget in Windows PowerShell? - Super User
You don't really need to download a file, only to activate that url, so perhaps there is an other command in the PowerShell. I don't know, I haven't used the PowerShell often.