Unfortunately the Harmony sends a RF signal to power on the TV, and there is no way to add additional power-on commands when I customize an activity. I have added a "Fix It" command to every activity that includes an additional TV power-on command. I can send that command as many times as I want. Sometimes it works, sometimes it doesn't. I have to use the OEM remote to turn on the TV.
This has happened only once, but my wife couldn't get an activity to work because the TV wouldn't get set to the HDMI 1 input. I even tried using the Device menu on the Harmony but that wouldn't work. I had to use the OEM remote and push the input button to cycle to the HDMI 1 input. If I hadn't been home she wouldn't have been able to watch TV. It would have been a real frustration.
I think I'm going to have to buy a new universal remote. I've got my eye on the SofaBaton X1 Universal Remote Control with Hub & APP.