If just mufflers and not header or AC change, should not need a tune. The stock system will "adjust" to a small change (muffler) but if you do anything else, you will need to tune. However, while it's not a requirement, a good tuner should make any stock bike run better. If you still have warranty (factory or extended), would be a good idea to go with an HD approved product (SE tuner) if you did decide to tune and have the dealer do it for good records. Warranty is everything on these CVO's.....
Sorry, but I disagree heartily with that advice. First, ANY change to the stock calibration (map) other than one approved by H-D and the EPA, will technically void the powertrain warranty, no matter what device is used. Read Harley's own info on the SEPST, it is for off road use only and illegal for street use. The SEPST flags the ECM when you change the map, and from that point on it will report the fact you have a non-approved calibration whenever a dealership hooks the bike up to the computer. Harley receives that data and could easily use it to deny a warranty claim if they want. It's not the dealers decision to make, the warranty is from H-D. As for the ESP, once again that decision isn't the dealers to make, the ESP administrator controls it and they tend to be much more strict lately than Harley is under warranty. ESP isn't covered by federal warranty laws, so they can void coverage much more easily than Harley can under warranty.
If you are seriously worried about warranty, a smarter approach would be to avoid the SEPST and use one of the devices that allows you to reinstall the stock map before you return to the dealer for service. The two I'm aware of that will do that are the TTS and the PV.
Jerry