With a blueprint, will BookyAI still change my chapters or their order?

No. From version 1.9.18, a book created from a blueprint with chapters is not planned again by the AI. The outline is written directly from your blueprint, in your order, and the progress line says "Using your blueprint: N chapters, as agreed". Each chapter gets what you agreed for it ("It must include", "Leave out", your story) as binding instructions, visible later under "Instructions" on the chapter. Your premise, the way the book is written and the exact facts and terms go into the Codex, which the AI reads for every chapter. The number of chapters set on the Structure step of the form is not used for such a book; a green note on the last step confirms it. On the book's page, the label "from your blueprint" saves the blueprint file again.