I dont think you should have too many problems with your warranty,have a quick word with your dealer.And for that price($355 sale price)plus postage you'd be as well getting the cat replacement pipe-looks so much better too.
I got my dealer to fit mine as it can be a bit fiddly.
The only problem with the replacement pipes so far are around the bracket which secures it,a couple have cracked,on mine it sheared the securing bolt,
there could be a couple of reasons for this,the cat is fixed with rubber mounts whereas the pipe is bolted solid and any misalignment will put a lot of stress on that area
http://217.199.188.40/xmb/viewthread...8&pid=249 944 I'm about to replace that one with a stronger bolt but also widen the whole in the mounting bracket so it doesnt exert as much pressure when secured.