In researching option codes specifically for the 550 Anniversary, today I learned that it was possible to order the "unique" exhaust from the 550 Anniversary on other Boxsters by ordering option code XLA "Polished stainless steel exhaust end". I happened across this option on this base 2004 Boxster sold on BaT two years ago. The pictures of the rear of the car show the Anniversary exhaust outlet and the build sticker under the hood shows option XLA.
Here is the link to the auction.
https://bringatrailer.com/listing/2004-porsche-boxster-21/
I have seen the Anniversary exhaust outlet on at least one other 2004 Boxster S listed for sale online and always assumed they somehow managed to get one from a salvage car or otherwise. I didn't know option XLA was available for all Boxsters. Curious now as to if it was limited to 2004 Boxsters only. Anyone know?