For the record, I have called Hyundai Canada regarding an aftermarker BOV install. The lady on the phone was very nice and said that no, changing the BOV would not void the warranty for the REST of the car, unless what is broken is a direct result of the BOV. And for what it's worth, in 2004 I bought a brand new Mazda3 2.3 and installed a cold air intake. Not too long after, I threw a CEL and brought it to the dealer. A wire was loose on the MAF sensor, which was plugged on my CAI, and their repaired it under warranty without any questions.
Also might want to keep in mind that Hyundai dealers (at least in Canada) DO sell aftermarket parts for the 2010-2012 coupes, and they are waiting for aftermarket parts to be available for the 2013. A little bit hypocritical to sell parts that would void your warranty don't you think?