According to Subaru, anything that you put on the car that was not listed on the original invoice when purchasing the car will void your warranty. It's interesting to note, however, that you can buy "SPT" parts from Subaru, have them installed, and even include them in your purchase price for your car, but you have to sign a paper stating that you realize those parts "may void your warranty".
Yes. The Magnusson Moss warranty act. However, what they can do is keep dodging you while you go higher and higher up in the Subaru organization, until finally you get tired of dealing with it. I have heard of more than one case where a customer filed a lawsuit against Subaru, and Subaru drew it out over two years.
Basically, just remember if you are going to do any major modifications to your car, you won't be able to get any warranty work done.
trust me man once you do one mod ## gonna go wrx crazy, i said the same thing at first and then when i did my exhaust one thing led to another and i havent looked back. if your that worried about the warrany maybe you should off for a little bit. i havent had any problems with the mods i have done yet.