I have a good understanding with my Service Manager. My delaership fitted all the parts, so they know exactly how the car is set up.
My Service Manager is a very sensible & reasonable person (just as I am). If parts break asa result of the lowering, I would expect that it would be covered under warranty. If on the other hand, parts (such as bushes) start to wear out faster as a result of the lowering, I am quite happy to put my hand in my pocket and pay the replacement.
It has to be done in a sensible manner, and I am lucky that I am dealing with a very reasonable young man.
I would thinkthat the car should still corner just as flat, but whether it would keep the tyres on full contact with the road over bumps and stuff is another matter.
Abyss (156 owner from Melbourne) had his car lowered with the Springs only. I am sure if you contact him, he will give you his opinion, as I have taken him for a ride in my 147 as a comparison.
Also note that the standard dampers will be compressed by a certain margin permenantly as a result of the lowered springs. This will more than likely shorten the life of the original dampers, so keep that in mind too.