Slavery is a biblical law. There are many laws concerning how to deal with slaves. See the laws of slavery in Maimonides. It is a whole book. And the laws of the Bible are forever. There is nothing to indicate that the laws were temporary. The very last of the prophets Malachi ends his prophecy with "Remember the Law of Moses." The whole idea that the Law can be abridged when it says openly that it is forever is ridiculous.  Besides the fact that it says by the laws that they are forever like Tzitzit and Chalah, there is the verse  הנסתרות להשם אלהינו והנגלות לנו ולבנינו לעשות את כל דברי התורה הזאת

And for what purpose would there be a document that you can change its meaning at will? There would be no function for such a document except to give power to the people that claim to understand it and represent it and get money because of their supreme holiness.
A document that's meaning can be changed has no legitimate function in the first place.
We have to say the the Torah has a meaning that is independent of interpretations. And it is only upon us to discern than meaning, not to change it.