I need to flush my power steering system and change my power steering pump on 2008 Suzuki XL7 Luxury AWD. How do I disable the ignition system to prevent car from starting while being cranked?

I would just unclamps your lowest line and let it drain, replace pump then put line back on and refill system with front wheels off the ground turn steering wheel left and right lock to lock with someone outside keeping fluid full for you. You could drive it a few days and get a turkey baster or a siphon kit and remove the fluid from the reservoir and put new in. Doing this a few times will ensure new fluid. I have done this and have never lost a pump or a rack.

Just an extra note- my 08 XL7 power steering kept failing until I added a magnet to capture metal particulates in the fluid. I used zip ties to attach the magnet to the dip stick so that it is submerged in the reservoir. New pump and fluid will work only temporarily with no magnet added.