well any mod has a chance at voiding your warranty if the dealership can prove that mod was specifically responsible for causing whatever problem you are claiming. but say your power windows stopped working, they are going to have a hard time proving your cams caused that to happen.

as far as practicality is concerned, cams are a pretty hard core mod in some cases. they can make you idle unstable and you motor louder, but i doubt these cams are that extreme. pulley's are probably the most practical. all they do is put less wasted power toward your accesories, like ac, so they dont steal power from your engine. i just woke up, so im pretty sure this was a crappy explanation. ill try and do better later.