I have:
A - watch tv
B - watch Roku
My sequence is to press A then power. This turns every component on, tv, cable box and soundbar. The power button on activity A for power up does: TV power on, cable power on, soundbar toggle, tv input HDMI 1. The rest of the remote buttons control the cable box an soundbar.
To watch Roku, I press B then power. The power button under B s set to change the tv input to HDMI 2. The rest of the buttons are programmed to control the roku and the soundbar
To go back to watch cable, I press the power button agan under activity B, but without pressing the B button. On power down under B, the power button changes the TV input to HDMI 1. I then press the A button (but not the power button), which allows me to control the cable box again.
To turn everything off, I use the A activity and the power button. The power down option is set to: tv power off, cable power off, soundbar power toggle
to watch cable: A - power button
to watch roku when the system is off: A - power button - B
to turn off from watching cable: power button
to turn off form watching roku: power button - A - power button
I would think you could add Kodi the same was to C, using the A activity to power everything on/off
This seems to be working for me so far. I did not want to sacrifice any of the other buttons for powering things or changing inputs, especially when we can use macros for multiple commands. I feel like I want/need more buttons coming from the Harmony One remote. I haven't found a better way to set this up yet, at least without more buttons to program or long presses.