Hebrews 7:12 can be believed in what it says plainly at face value.
It is true.
The word use can also be translated as "transition", so I agree that it can be believed in what it says plainly at face value, and I've made arguments for why it is appropriate to translate it that way and inappropriate to translate to have the meaning that you suggest. God's righteous standard is eternal (Psalms 119:142) so therefore also are all of God's righteous laws (Psalms 119:160), so it is not speaking about them being changed.
Jesus said turn the other cheek instead of an eye for an eye.
Jesus said love your enemies instead of hate your enemies.
Whenever Jesus quoted Scripture, he proceeded it by saying "it is written", but when he was quoting from what the people of his day had heard being taught about Scripture, he proceeded it by saying "you have heard that it was said", so the emphasis is on the form of communication. So Jesus was not speaking against what was written, but against what they had heard being taught about it. For example:
Matthew 5:43 “You have heard that it was said, ‘You shall love your neighbor and hate your enemy.’
While the Law certainly instructs us to love our neighbor (Leviticus 19:18), it does not instruct us to hate our enemy, so Jesus was simply correcting what was wrongly being taught about the Law, not sinning in violation of Deuteronomy 4:2 by adding his own commands.
Peter was told to eat unclean animals which was a violation of OT Law.
Peter was never to eat unclean animals and if he had tried to say that it was now acceptable, then then people would have been quicker to reject him as a false prophet than to accept that it was now acceptable to eat unclean animals, as should we, but he gave the interpretation of his vision three times and not once did he even hint at unclean animals now being acceptable to eat. It says in Peter's vision that all kinds of animals were let down, so he could have easily obeyed the command to kill at eat by simply killing and eating one of the clean animals, and the point that God was making to him was about why he refused to do that. The issue was that there was a man-made ritual purity law that said that things that come into contact with things are unclean become common (Mark 7:3-4), so because all of the animals were bundled together, all of the clean animals there had become common. So by stating that he had never eat anything that was common or unclean, he was saying that he had never broken this ritual purity law or kashrut, and he correctly refused to eat an unclean animals, but by refusing to eat one of the clean animals, he was disobeying God in order to obey man. Note that God did not rebuke him for referring to clean animals as unclean, but for referring to clean animals as common, so his vision was in regard to the mislabeling of clean animals, which he interpreted as being in regard to the mislabeling of Gentiles, and had absolutely nothing to do with God's eternal laws being done away with.
The animal sacrifices and the priesthood had ended with Christ's death when the temple veil was torn.
In Acts 18:18, Paul took a Nazarite vow, which involved making offerings (Numbers 6) and in Acts 21:20-24, he was on his way to pay for the offerings of others who had taken a similar vow in order to disprove false rumors that he was teaching against the Law and to show that he continued to live in obedience to it. Furthermore, the Bible prophecies a time when a third temple will be built and when offerings will resume (Ezekiel 44-46).
Paul says in Galatians 5:2 that if you seek to be circumcised, Christ shall profit you nothing.
Nowhere does God's Law require all Gentiles to become circumcised in order to become saved, and if God did not require it, then it is therefore a man-made requirement. Though God did require all Jews to become circumcised, not even they were required to do so in order to become saved. By becoming circumcised, Gentiles were becoming Jewish proselytes and agreeing to live as Jews according all of their oral laws, and doing so in order to become saved. If they were trying to become saved by their obedience to man-made laws rather than by faith in God, then Christ would profit them nothing. Paul said that circumcision has no value, but that what matters is keeping God's commands (1 Corinthians 7:19) and that circumcision has much value in every way (Romans 3:1-2), so the key is that the value of circumcision is entirely dependant on whether we keep the Law, and the way to tell that a Gentile has a circumcised heart is by observing their obedience to it (Romans 2:25-26).
Paul says we are not under the Law.
I agree that we are not under the law, but Paul specified in Romans 6:14 that the law that we are not under is one where sin had dominion over us, which does not fit at all with God's holy, righteous, and good law, which Paul said was not sin, but revealed what sin is (Roman 7:7, Romans 7:12), but rather it fits perfect with his description of the law of sin. It wouldn't make sense to say interpret Romans 6:14 as referring to us not being under God's Law and then say in the next verse that being under grace doesn't mean that we are permitted to do what God's Law reveals to be sin. Rather, in Psalms 119:29, David asked God to be gracious to him by teaching him to obey His Law, so if we are under grace, then we are under God's Law. Furthermore, all of the surrounding context of Romans 6:12-19 supports obedience to God's Law, where we are not to present ourselves as instruments of sin, but as instruments of righteousness, that we are to be slaves of God, not slaves of sin, and that we have been set free from sin in order to become slaves of righteousness, and that we are no longer to present ourselves as slaves of impurity and Lawlessness, leading to more Lawlessness, but as slaves of righteousness leading to sanctification.
This would be the Old Law given to Israel and not all forms of Law (like God's Eternal Morals Laws after the Fall, and the Laws given to us by Jesus and His followers).
Morality is in regard to what we ought to do and we ought to obey God, so all of God's commands are inherently moral commands. Jesus was sinless, so he at least taught his followers how to walk in obedience to the law by example, which would have been included in everything that he had taught them as part of the Great Commission, and as his followers, we are told to follow his example (1 Peter 2:21-22) and to walk in the same way that he walked (1 John 2:3-6).
All ceremonial laws given to Israel were for Israel and they are not for the church or believers today. So commands like the Saturday Sabbath and circumcision and the dietary laws and animal sacrifices do not apply to us today (No matter how you may want that to be).
The Greek word "ekklesia" is translated as "church" or "assembly" and is used many times in the Septuagint to refer to the assembly of Israel in the wilderness, so Israel, the people of God, and the Church are all synonymous. According to Romans 9:6-8, Israel is made up of those who have faith in the promise, in Ephesians 2:19, Gentiles have become fellow citizens of Israel through faith in Messiah, and the 1 Peter 2:9-10, Gentiles are now included among God's chosen people, a holy nation, a royal priesthood, and a treasure of God's own possession. God has given instructions to His followers to teach us how to walk in His ways and as his followers, we should seek to follow those instructions and to learn how to walk in His ways. Israel was intended to be a light to the other nations to teach them about God and how to walk in His ways (Isaiah 2:2-3). In 1 Peter 1:13-16, we are told to have a holy conduct for God is holy, which is quote from Leviticus where God was giving instructions for how to act in accordance with His holiness, so ceremonial laws are not particular to Jews, but are particular to God. They are his ways, not the ways of the Jews. It should be relatively straightforward that having a holy conduct involves keeping God's holy days.