No it does not void your warranty unless the mod part is the direct result for the issue. IE. If you install a CAI and your transmission fails, your transmission will be fixed under the warranty as the CAI has nothing to do with it.
Now if you install a boost controller and blow your engine, then yah your warranty might be voided IF they can prove you had a boost controller or you're stupid enough to leave it on for warranty work. Until you really start doing big things (FMIC, New TMIC, Bigger Turbo, Non-PiggyBack ECU, ETC.) that you don't remove prior to taking it in for Warranty work, you really don't have to worry so much.