Originally, Freddie Mercury was supposed to be at the pool party, but Queen said no. They did, however, allow an appearance by John Deacon, which worked out as Deacon was the one who wrote "Another One Bites the Dust", which is not mentioned in the scene but Deacon's insistence on that song being parodied by Al puts more emphasis on the satirical portrayal of Deacon as a self-centered semi-celebrity.
Daniel Radcliffe actually learned to play the accordion for the film. He first took lessons from a friend, then 'Weird Al' Yankovic himself while on set. He admits to not playing very well, but passable enough for the movie.
Inspired by Weird: The Al Yankovic Story (2010), a "Funny or Die" short starring Aaron Paul as Al and Patton Oswalt as Dr. Demento. 'Weird Al' Yankovic himself appears in the short playing a similar character to the one he would play in the full-length film.
Patton Oswalt originally was going to reprise his role as Dr. Demento from the Funny or Die Presents... (2007) short but suffered a broken ankle. Three days before filming, they were able to bring in Rainn Wilson.
Daniel Radcliffe was chosen by 'Weird Al' Yankovic partially as a result of seeing him sing The Elements on The Graham Norton Show (2007). The performance had stuck in his head and when they started casting, Daniel was his first choice.