Also, there will most definitely be ways to achieve 500HP on a 425Hp LS3 without voiding your factory warranty.
Not to mention that you can indeed have the modifications I previously mentioned and still have some kind of a warranty as there are a great deal of tuners and dealers that will supplement their own warranty for any parts that are not covered under the factory warranty. Albeit, it may not be a 5yr/100,000 mile warranty.
For example....
http://lingenfelter.com/GTO366LS2.htm
That is on an LS2 GTO, but it illustrates my point. At the bottom you will notice they back their work with a 3 year/36,000 mile warranty.