These are common fitments, but they are aftermarket changes just like a remap – your tow-bar does not invalidate your warranty so why should your remap? However, manufacturers, of course, have the right to investigate and possibly reject a warranty claim if the failure is directly related to and caused by the tuning (remember not all tuning is the same quality as AMTuning). Therefore, for your total peace of mind, AMTuning offer a back to stock service to try to mitigate these awkward conversations with the dealer when under warranty.
AMTuning give a lifetime software guarantee too for reinstallation should your ECU get reverted back to standard. Should you lose your tuning files due to dealer actions or parts failure your dealer will be happy to re-install the map on to your car free of charge for as long as you own the vehicle, there may be a small surcharge for fuel subject to distances.