You ask good questions and it is obvious to me that you are a thinker. No, universal truths do not change over time. Spiritual truth is eternal and it will never change;
it is faith, knowledge, certitude, justice, piety, righteousness, trustworthiness, love of God, benevolence, purity, detachment, humility, meekness, patience and constancy.
However, the second part of religion which refers to the material world changes with every new religion that is revealed.
“The second part of the Religion of God, which refers to the material world, and which comprises fasting, prayer, forms of worship, marriage and divorce, the abolition of slavery, legal processes, transactions, indemnities for murder, violence, theft and injuries—this part of the Law of God, which refers to material things, is modified and altered in each prophetic cycle in accordance with the necessities of the times.” Some Answered Questions, p. 48
The current Messenger of God defines the social teachings and Laws for the current times. According to Baha’i teachings, the assumption has to be made that if a new Messenger brings a new revelation and He was sent by God, whatever he revealed is identical with the Will of God. We might not agree with the Messenger, but if we argue with it that is as much as saying we think we know more than God about what is moral and what is in the best interest of humanity collectively.
People have had to jump through different hoops in different ages to be in line with God's will, which is for their own good, because God reveals teachings and laws that are in humanity's best interest.