The kit will be street legal and warrantable, even in California, as long as you don't vary from the parts in the kit and only use the emission legal ECM calibration download that comes with the kit. As soon as you change to different parts, like cams for instance, or use a calibration other than the approved legal one, the bike is no longer street legal and the warranty is also void. So it's just like the stock engine; if you modify it or have it tuned it won't comply with EPA certifications and will therefore be illegal for highway use, and the warranty can be voided at Harley's discretion (or the ESP at the ESP companies discretion). The following is from H-D in the description of the kit:
"These Screamin' EagleĀ® products are 50-state street-legal for sale and use on all vehicles, including those that are pollution controlled. Complies with the requirements of 40 CFR Part 86, subparts E and F."
Jerry