Had a few problems, not sure if its do-able.

If you have no idea what is Tomato(or FreshTomato), please check it out
https://freshtomato.org/

This is the USB relay.
https://shopee.com.my/-Ready-Stock-LCUS-1-U...ea-adbcc249a201

Can i write something small into the FreshTomato router ? I know its a firmware and it should be read-only, but i also know it has some storage for log files, not sure where its, maybe its RAM, so if its possible, does it mean i can store some small file into its RAM and execute it ? I dont mind everything is lost if there is a power failure or reboot. Best is it maintain the file after reboot/power outage.

Whats that file for ? its some kind of program that manage to communicate with the USB relay.

https://github.com/darrylb123/usbrelay

So my plan is send signal within the network, to the router, then the router communicate with the USB relay to turn something on or off.