The Iron Throne has been greatly redesigned from Game of Thrones (2011). It is larger and more asymmetrical to more closely match the description in George R.R. Martin's novels, although it is still nowhere near that big: the throne in the books is a 40-foot, immovable, asymmetrical behemoth made from 1000 swords welded together, with the seat 20 feet above the ground, and only accessible by a flight of stairs; the person sitting on it addresses people down below from 40 feet away.
In Season 1 of Game of Thrones (2011), George R.R. Martin, the author of A Song of Ice and Fire, wanted his prop head on a pike, but due to budget limitations they couldn't afford it back then. In a recent podcast, Ryan J. Condal (Showrunner of House of the Dragon) promised Martin that his head will be seen in House of the Dragon.
Paddy Considine stated Viserys' disease is a form of leprosy, and "It becomes a metaphor for being king, and the stress and strain that it puts on you, and what it does to you physically, what it does to you mentally."
The Valyrian steel dagger carried by Viserys is the same one that is used in the attempt on Bran's life in the first season of Game of Thrones (2011), as well as used by Arya in the final season. Despite its significance in both shows, the dagger is rarely mentioned in the "A Song of Ice and Fire" book series, and is not mentioned at all in "Fire & Blood."
Like its parent series, Game of Thrones (2011), House of the Dragon (2022) portrays many of the characters as older than they were in the source material. King Viserys is portrayed as an aging man with graying hair (actor Paddy Considine is almost 50). Rhaenyra is shown initially as at least a teenager, perhaps a bit older. In the source material, Viserys was not yet thirty when his wife Aemma died, and Rhaenyra was only 8 years old when she was proclaimed as Viserys's heir. On the other side, Alicent was aged down to be Rhaenyra's age, whereas in the books she was about a decade older. Criston Cole is also portrayed younger here than in the books, where he's Daemon's age.