If you can lower the front also, the handling should not be effected very much in a negative way..It should shorten the wheelbase making it corner better, by lowering the whole machine. cornering clearence is effected..
I would not just lower the rear and not the front..Unless I was just doing highway driving...
Raising the rear will make the bike turn in quicker, but what does it effect in high speed stablity? All inline 4 bikes are too tall already..