To the OP's question, if one does a mod that goes south, Subaru can decide to deny warranty claims for "directly affected" (my words) parts on your car. And as posted above, we are small fish compared to a large corporate entity, so if a dealer decides not to honor your warranty claim, you have the right to appeal that decision a level or two above, but if Subaru corporate decides in the end to still deny your specific claim, who among us can afford to get a lawyer fight their decision in court. Guessing that less than 1% of us clubWRX members could afford to do that.
So if you do a mod, and I have done 30+ mods on my 2017 WRX, we have to accept that if a related part goes south, we are the ones who will pay to get it fixed. As an example, I installed a Perrin steering dampener on my '17 WRX, and if my steering rack or any other part of my steering system goes south, I would not fight a warranty denial, i.e., I made a mod choice/install, and I accept the consequence of that mod. For each and everyone of my mods (and BTW, here is my "build thread,": http://www.clubwrx.net/forums/builds/134543433-wrx-johns-2017-build.html
), I accept responsibility. Does not mean that if my motor goes south (I have not even touched it), and my dealership blames my Corsa exhaust that I would not fight it, but IMO, doubt that that would happen.. However, will I change on tiny part of my intake, do even a stage 1 tune on it before my warranty is over, "no."
I admire others who are willing to take on more risk than me. We each get to choose our own level of risk, and as long as we all know that for every non-visual mod we do, that there is risk we are willing to take, we can all proceed on that basis.
As to the very detailed part/question in your thread, changing even a part of an intake system has resulted in significant later motor problems for some, especially
for those who then choose not to have their car tuned by a pro. And yes, even some intake system changes which have then had a tune by someone who is a experienced tuner and who operate a for-profit business as a tuner, has resulted in occasional problems.
Again, we each get to choose the level of risk we are comfortable with. And BTW, I have modded several other cars over the past few years, and it is not just Subaru who can/does deny subsequent warranty claims -- resulting in an unhappy owners. On the other hand, all cars these days are precisely engineered systems, and can you deny, for example one circumstance I know of, Ford Motor Co for denying a claim for a blown motor when the owner supercharged his factory un-blown motor to around 18 PSI?