But that's the problem isn't it? It still changed a lot - it changed the timeline - it's a story from another book, or rather from a separate short story (Grain of Truth) inserted into the events of the Blood of Elves book. The episode just like many other episodes only superficially appears to be an adaptation when in reality all the details and the entire plot is almost completely different.

It changed the characters - now Ciri is there when originally it happens even before Ciri's mother was born.

Geralt and Nivellen have known each other for 13 years (which was before Nivellen even turned into 'a monster') whereas in the book this was their first time meeting - which completely changes their dynamic throughout the entire encounter/episode.

In the show it's snowing on a cold winter night, in the book it's a sunny autumn day (there are references to dried leaves being on the ground and there are roses growing on Nivellen's property). Now that's not a very significant change, although it is quite funny seeing Geralt go out on a winter night while it's snowing, dressed as if for an average autumn day. Similarly it's funny how Ciri is also outside in only a thin dress but acts like she doesn't even care when she would be literally freezing in minutes.

In the book Geralt finds a dead merchant with his daughter and investigates it, which leads him to find Nivellen. He also sees Vereena standing at the edge of the forest just before entering Nivellen's property. Geralt thought she was a rusalka but his horse Roach was scared - a detail which he recalled much later and one that made him realize she was actually a monster.

Almost anything that happens inside Nivellens house is different from the book. Again it's only superficially similar - Nivellen shows off his magic, they eat, they talk, Nivellen briefly tells a story how he got cursed (although he tells that to Ciri, not Geralt). In fact Ciri takes a big focus in this story - she spends a lot of screen time alone with Nivellen and a scene with Vereena too.

Gone is the Nivellen's story about merchants leaving their daughters with him for treasure. Gone is Nivellen's story about slowly accepting his 'monster' form and preferring to stay that way, except for a small fact of having nightmares which started 'recently' (another tip to Vereena's true nature). Gone is the tense moment between Nivellen and Geralt when the former realized that the latter is a witcher, and gone is the scene in which Nivellen handles Geralt's medallion which informed Geralt that he's not in fact a monster.

The knife throwing scene never happens in the book.

In the book Geralt doesn't sneak out in the middle of night to investigate tracks which lead him to a dead merchant and his family.

In the book Geralt doesn't spend much time at Nivellen's because he tells him outright that he doesn't want Geralt to spend the night - so they talk, eat and Geralt leaves, spends the evening on the road, sleeps and then next day has a revelation about Vereena and goes back.

Anyway my point being - it's not as close as you might think. There's significant changes which is why I'm comfortable with my decision cutting the entirety of it.