Does it matter?
The context of language at any point in history is of primary importance when trying to understand the ramification of a word.
There was a debate about the two words, as originally written by Jefferson, who at first used the word inalienable to describe the rights that naturally flow from a humans' mere existence. His choice was based on his personal beliefs, which while not atheistic, precluded a belief in a personal creator from whom natural rights flowed. Today he'd be called agnostic. Some would argue that Jefferson original word should be used, but that is sophistry, and a moot point, the truth is the word unalienable was a definite choice that was ratified unanimously at the time and not subject to revision without a Constitutional amendment.
The fact is that, Jefferson and John Adams both understood that there is a distinct difference between what Jefferson was saying and the intent of the Declaration of Independence. INalienable rights come from the government and pertain to civil rights. UNalienable rights come from a higher source of life that cannot be given or taken away. To be clear Adams viewpoint won the day and UNalienable was used and unanimously adopted by the Framers.
They did not say anything they did not intend and they were precise to a fault. That is why its important--they were writing this document for us, their progeny.
As understood by the framers at that time.
INalienable is a right that can be given or taken away it can be bought or sold, in those times, it literally meant, property that could be placed in (a) lien (offered as security). It was transitory. It was the argument used by pro slavery advocates, to buy and sell African-Americans, who were considered property, sub-human, a class apart from the protection, set forth in the Declaration and therefore not subject to the Human Rights.
UNalienable is a right that cannot be taken away. It was a right that was and is un (a) lien able (it was fixed and unassailable). It was irrevocable, never to be taken away.
Given the fact that this Declaration was a condemnation of the monarchy's right to grant or not grant rights to his subjects the framers wanted to make sure that it was crystal clear that they rejected that presumption outright and choose UNalienable to ensure that distinction.
Today we act as though the two words are synonymous but within the context of history these two words had significant and different ramifications. To be sure there is a deliberate attempt by the far right to obscure the difference, which makes it even more important to preserve the Declaration as it was written.
Human rights are universal rights, or status, regardless of legal jurisdiction or other localizing factors, such as ethnicity, nationality, and sex--that by their nature cannot be taken away, violated, or transferred from one person to another. They are considered more fundamental than INalienable rights, such as rights in a specific piece of property.
The debate over Prop 8 is about that very distinction.