Matty is spot on, I've been through this with a warranty claim on a previous claim. Warranty is only voided if the moficiation can be DIRECTLY attributed to the problem. eg if Ric had lowered his car, they couldn't deny the engine replacement because it was 'modded'.
If Ric had fitted a supercharger to his engine then they have grounds to void the warranty.
Wheels/suspension/stereo and exhaust usually are OK. Modding the ECU, upping the boost and doing engine mods then claiming a gearbox under warranty won't fly. Increasing the engine output directly affects gearboxes, clutches, driveshafts etc. Seen subaru deny warranty on this with severla WRX's and Foresters. HTH