Tons of things will void your warranty. Bolt-ons and stuff that doesn't require you to open up your engine or splice into wiring will not.
As for your HID kit, please do NOT put a set of bulb rebased HID capsules into your stock housings. If you're going to put HIDs into your headlights, retrofit true HID projectors into place. HID rebase setups (almost all HID "kits") don't put light in the right place in a housing that's meant for incandescant bulbs. They throw glare everywhere, they can get you some pretty hefty fines (cops look for these), and they give a bad name to the people who want to properly fit HID projectors into their stock housings.