As far as meaning, they are the same. Look up one and it gives the other as part of the definition. This is from Mr. Google: “The unalienable rights that are mentioned in the Declaration of Independence could just as well have been inalienable, which means the same thing. Inalienable or unalienable refers to that which cannot be given away or taken away.”
You are right; the final document contains unalienable. However, the first drafts used inalienable, and historians report that was Jefferson’s preference.
And I totally agree with you in regard to the piece — beautifully written! Thank you, Robin.