heh in my opinion doing any sort of performance modification AND expecting the manufacturer to warranty engine/clutch/gearbox/whatever is pretty foolish. Sure you can plug in a Racechip or JB4 and remove it before it goes in for a service etc, but the warranty doesn't cover that. Also as someone who's studied metalurgy and mechanical engineering (and my father was a professor of both and regularly consulted with car companies on a variety of areas) if you do mechanically damage to an engine or gearbox, it's actually not that difficult to figure out why it happened (increased boost pressure, lean mixture, etc etc)
For example, the DCT in the forte is rated to around 250ft-lbs of input torque. The stock engine puts out around 195ft-lbs - that's a safety margin of 25% and it would be highly irregular for the DCT to have any sort of mechanical failure at those torque levels. However, plug in a Racechip or similar and run the car at one of the higher settings and your torque output from the engine will be over the level the gearbox is rated for. It's trivial for a metalurgist to look at a broken gearset and visually see why it failed.
I'm all for modifying cars and increasing performance and so on, but if you're going to do it then you do so at your own risk. And if a car isn't fast enough/has enough power it can be traded-in for something that does (an I30N or Veloster N, for example).