I've looked into this before...
You may have to define what OFF will actually mean.
An external Latching Relay is ideal, because you will not waste any power for the coil while the system is ON.
However, once you send a data pulse to change the system to OFF, there is no power available to allow an ON data pulse to restart the system.
If you are willing to accept an IDLE Current for a power supply that will "always be on",
then this will work (meaning that the remote system will never be 100% in an OFF state), assuming using data pulses.
The other option is to actually send a stronger Power Signal (not just a data pulse)
to trigger the latching Relay from OFF to ON. Enough power (V & I) will be needed to actually actuate the COIL on the Latching Relay.
I have seen Remote Controlled Power Strips which may solve your problem, too.
If you actually NEED to "Operate a Switch" (such as in a test stand),
then I've used two solenoids, each solenoid having a rubber-tipped plunger,
and mount & control each solenoid (one for ON, one for OFF) as needed.