This topic has been covered in many threads here and on other forums. Bottom line, NO, lifts and other mods do not void your warranty. However, the manufacturer doesn't have to cover either the modification itself, or, and here's the rub, damage to components caused by a modification. So, if a wiring harness or on board computer fails due to an aftermarket electronic component or bad installation, "this Bud's for you" so to speak. Conversely, Jeep CAN NOT "cancel" your warranty if you install a lift kit or larger tires or other mods. All this is spelled out in Federal law.
'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.