Well, you can do small mods, and they shouldn't void your warranty. ALSO, if you do any such "bigger" mods, and made sure to keep all your stock stuff, you could return it to stock before taking it in for warranty work that may be needed
I'd start out with the usuals....
Catback, shifter, CAI (K&N FIPK), subframe connectors.....
SOme people will suggest gears, but if anything breaks in the drivetrain (tranny, driveshaft, rear-end) most dealerships will void your entire drivetrain warranty.
So, I'd just stick to the basics until you pass 36,000
Spend your time now gettin the exhaust and suspension ready for later mods
-Will