Depends on the dealer? The salesman at the dealer I bought it from was clueless, told me pretty much ANY modification "voids the warranty" including a tow hook (wtf?). Happily took my warranty business to another dealership. The foreman at the other dealer sang a much different tune, even taking the time to look up ways in which the clutch would be covered outside of the first year. Interestingly, I was informed the flywheel is part of the powertrain per VW's book and a reason such as "loose/worn flywheel" can be used by the dealership to fight for a clutch replacement as that "may" have caused the clutch to wear out (lol). I found that amusing.
He also told me that their specific dealership is mod friendly and does everything to fight for warranty claims as its not money out of their pocket (although an ECU tune that blows the engine or turbo is obviously much harder to fight for). Still, he emphasized that the specific modification has to cause the specific problem for VW to give them any issues. This was reassuring to hear. In fact, my clutch has been acting funny again (2K miles after a full replacement for slipping) and he even offered to throw in a brand new DMF, install an upgraded clutch of my choice, with the only cost to me being the clutch disc/pressure plate I decide to use. New DMF + labor + fluids = no cost. Or stock clutch/DMF replacement if I want.
Find a dealership, speak to the foreman in charge, and you'll get a sense of what lies ahead dealing with them. First dealer told me they wouldn't inspect my car off the bat if holes weren't drilled in the bumpers, another said "what catback, what mods, I don't see anything" lol gladly took my business to dealer #2.
Disclaimer: ECU tunes, engine mods, DPs, etc will be hard for even a mod friendly dealer to overlook given a major catastrophe. I'm sure a good one will go further to help you out but common sense says pay to play with these more serious mods. Catback should be zero problem outside of some crap dealership.
