To expand on raz-0's response which is absolutely correct, your warranty can't technically be voided. FCA can reject a claim on a single issue that they can prove was caused by something you added, but it won't void your warranty on the rest of the vehicle.
Also, the burden of proof is on them to show that your add on was the cause of the problem.
So I'd say bumpers are pretty safe. Add an aftermarket forced induction kit? Good luck with any drivetrain claims with that. No problem for warranty work on a busted radio, however, as one could not be blamed for the other.