Tom, the shock rate won't change when the air pressure is increased. It was likely the progressive spring rate change that messed up your handling; a higher rate as when the air shock is compressed will reduce the traction on that tire just like a rear sway bar that is too big, with the same result. I don't recommend doing any serious cornering with air in the shocks ("now he tells me").

Better fixes for the ride height issue are to install a spacer block or get the spring re-arced.