The Wedding Invasion was not the grand revelation of changelings to the world. True, only a few ponies knew of their existence before the incident, but changelings have been living in Equestria for years, and many ponies see them as a common part of their lives.
Sawtooth is a prime example of this: a musician who has lived peacefully in Manehatten for years, and is well-known in the music community as a fill-in for musicians who are... otherwise occupied.
Neon Lights gets predictably wasted, and Sawtooth fills in for him.
This story is about 87% dialogue. Be warned.