I have not argued that we earn our salvation as the result of having first been circumcised, and in fact I agree that that is not the case, but that we are saved by grace, so I have not refuted my own argument. In Psalms 119:29-30, he wanted to put false ways far from him, for God to be gracious to him by teaching him to obey the Mosaic Law, and he chose the way of faith by setting it before him, so this has always been the one and only way of salvation by grace through faith. There is a huge difference between the position that our salvation requires us to have first obeying the Mosaic Law in order to earn it as the result, which many verses deny, and the position that we our salvation requires us to be a doer of the Mosaic Law, which many support. For example, in Matthew 7:23, Jesus said that he would tell those who are workers of lawlessness to depart from him because he never knew them, in Romans 2:13, only doers of the Mosaic Law will be justified, and in Hebrews 5:9, Jesus has become a source of eternal salvation for those who obey him. In other words, the Mosaic Law was given to teach us what the content of God's gift of salvation is, not as a means of earning our salvation. Our salvation is from sin (Matthew 1:21) and it is by the Mosaic Law that we have knowledge of what sin is (Romans 3:20), so while we do not earn out salvation as the result of having first obeyed it, living in obedience to it through faith in Jesus is intrinsically the content of his gift of saving us from not living in obedient to it.
Do you grant that there can be both legitimate or illegitimate reasons for not following a particular law? For example, not even Jesus followed the laws in regard to having a period or to giving birth. The Israelites were given a number of laws had the condition "when you enter the land..." while they were still wandering the wilderness for 40 years, so there is not wrong with not following a law that can't currently be followed. Likewise, when the Israelites were exiled in Babylon the condition for their return to the land was to first return to obedience to God's law, which contained laws in regard to temple practice, which they couldn't obey because the temple had just been destroyed, so God honored their obedience to the laws that they could obey. There are legitimate reasons, not making excuses.
There is a difference between the instructions that were given during the first Passover and how it is cerebrated afterwards in accordance with Deuteronomy 16:1-8. The issue of what I am personally doing is independent of the issue of whether followers of God ought follow what He has commanded in accordance with the example that Christ set for us to follow, so even if I were living in complete disobedience to the Mosaic Law, then it wouldn't change the fact that followers of God ought to follow what He has commanded in accordance with Christ's example.