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I think everything is doable, if the reader gets the feeling it is fitting. I see no problem in the approach to have the book in first person and switch to third for the finale.
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/17777 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/