You can probably disable the Genesis solenoid by simply unplugging the connector on the Cole Hersee charge controller. The solenoid will never energize and connect the two batteries that way. If you ever need to combine the two batteries because the starting battery is run down, just plug the charge controller back in, and use the start boost button.
The DC-DC charger input power wire (from the starting battery) does need to be on its own ignition activated solenoid though, so it will switch off when the engine isn’t running. I’d put a fuse in the ignition activated wire close to the solenoid in an in-line fuse holder, and use that to disable the DC-DC charger in the event you need to combine the batteries.
:):)
