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Switching P.O.V. is the closest relevant trope. In this case the distinct change of tone and style helps the reader understand that this is a new person with a different take on the world. If the novel is entirely snippets from other characters, you may have a Scrapbook Story
"Rashomon"-Style covers stories where two or three different narratives tell the same series of events, often without resolving which one was the most accurate.

This is a style of narrative where the POV character will switch to being some random, useless NPC or redshirt for a scene and we'll see the protags from their perspective. I think it only happens in third person limited stories; it's similar to switching perspectives in a 1st person story but less dramatic. It happens a lot in Garth Nix's Old Kingdom trilogy and also in Snow Crash.
For example, there are couple of sections in Snow Crash where the POV character switches to one of the "ratthings"; the style changes dramatically because it's describing stuff that happens from the perspective of what is, for all intents and purposes, a dog. Instead of referring to protag Y.T. as Y.T., the dog calls her "the nice girl who loved him". It also happens when Hiro goes in to buy a motorcycle, we see everything from the salesman's POV instead of Hiro's, so we see what the salesman thinks of Hiro.
It happens a lot in the Old Kingdom trilogy with the people along the wall; you get a short introduction to Permitter Guard #914 and what he's up to before the heroes actually show up in the scene and something plotty happens.
It seems possible that this might have a term in literary analysis or it might have a trope page.