The installer mounted the solar kit controller box 10’ in the air instead of down at a level that is accessible like the instructions say. Can I add a remote switch on the battery input to your solar kit so that they can turn it off at the bottom of the pole?

No if you switch the battery voltage ON while the inverter is already switched to ON it will not always start up. This is the reason that the power switch on the inverter is used to start and stop the system and the reason that the controller box must be mounted in an accessible location.