I have not done that, but know many people have and they were successful, such as Can rachio open two valves to water a single zone? - Troubleshooting / Tech Support - Rachio Community
The two ways it can be affected:
- Not enough pressure: Obviously, you have done this before, so it will not be a problem for you
- Too much power (amps): It looks like you have a Pump/Master Valve. With this and two valves, you should not have any trouble with this either . . . unless POSSIBLY you have a rather old valve, valve about to go bad, or a high drain pump start relay. It you want to post specs, that might be helpful.
It is great to have the picture you posted, I would suggest running each zone before disconnecting to make sure each zone works, label the wires before disconnecting, and remember to configure the Pump / Master Valve. I would guess the two white wires at the bottom of the image going to the left side of the Hunter are for Common, which go to “C” on Rachio (3 “C” terminals exist, so you do not have to go in the same spot). Use the Rachio supplied power, not the Hunter power. If you have a sensor, I suggest not using that at this time. You can hook that up later, but many do not.