Maybe this is for another thread but does a flash pose any threat to voiding the warranty? Actually what mod can produce warranty issues?
This has been discussed in the past. There is no official word, that I know of. Generally, a dealer is not going to know you had your ECU flashed, unless you tell them. They have no tools to know it is any different (I don't believe our firmware is "signed" or checksumed.... but that is probably already being done in some vehicles now). I don't recommend putting a sticker on it or anything like that, advertising it, however.
Generally, a dealer or factory cannot void your warranty for work and mods you do yourself, without provable cause. They can (and sometimes do) claim that if you do not perform the recommended upkeep or use an aftermarket part, that it is not covered. But my understanding of the law is that they would have to have proof that your actions or negligence CAUSED the problem. They can't automatically just assume what the customer did is at fault. Of course, that doesn't mean you won't go through lots of harassment, wasted time, and possibly even legal action in the process.
The reason there is significant performance improvements available with flashing is exactly because the engine is designed to meet regulations about noise, fuel economy, and emissions control (and the manufacturer also adds things like drivability and reliability, too). Reflashing throws all that out the window, so it is quite illegal
But replacing the muffler with a third-party one is also illegal; as is adding HID bulbs, adding additional driving lamps, replacing a lens with a third-party, wearing earphones, using a too-darkly tinted visor, and driving over the speed limit. I don't suppose anything would be very much fun if the dealer acted as a legality spy (other than during a state inspection, and those tend to be a joke).