Did God ever accept a sacrifice that was against His own law?
The short answer is no if offered to pagan gods which are none other than demons.
The Scriptures are quite clear on this!
3 Thou shalt have no other gods before me.
4 Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth.
5 Thou shalt not bow down thyself to them, nor serve them: for I the Lord thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me. - Exodus 20:3-5
We should likewise keep St. Paul words in our minds:
…19Am I suggesting, then, that food sacrificed to an idol is anything, or that an idol is anything? 20No, but the sacrifices of pagans are offered to demons, not to God. And I do not want you to be participants with demons. 21You cannot drink the cup of the Lord and the cup of demons too; you cannot partake in the table of the Lord and the table of demons too.… - 1 Corinthians 10:20
Yet even Pagans seem to do God’s bidding at times, as when he spoke about the unknown God at Athens.
According to the book of Acts, contained in the Christian New Testament, when the Apostle Paul visited Athens, he saw an altar with an inscription dedicated to that god (possibly connected to the Cylonian affair), and, when invited to speak to the Athenian elite at the Areopagus, gave the following speech:
22 Paul then stood up in the meeting of the Areopagus and said: “People of Athens! I see that in every way you are very religious. 23 For as I walked around and looked carefully at your objects of worship, I even found an altar with this inscription: to an unknown god. So you are ignorant of the very thing you worship—and this is what I am going to proclaim to you.
24 “The God who made the world and everything in it is the Lord of heaven and earth and does not live in temples built by human hands. 25 And he is not served by human hands, as if he needed anything. Rather, he himself gives everyone life and breath and everything else. 26 From one man he made all the nations, that they should inhabit the whole earth; and he marked out their appointed times in history and the boundaries of their lands. 27 God did this so that they would seek him and perhaps reach out for him and find him, though he is not far from any one of us. 28 ‘For in him we live and move and have our being.’[a] As some of your own poets have said, ‘We are his offspring.’
29 “Therefore since we are God’s offspring, we should not think that the divine being is like gold or silver or stone—an image made by human design and skill. 30 In the past God overlooked such ignorance, but now he commands all people everywhere to repent. 31 For he has set a day when he will judge the world with justice by the man he has appointed. He has given proof of this to everyone by raising him from the dead.” - Acts 17:22-31
Now the OP mentioned the following:
Now granted it wasn't just a human sacrifice, but Jesus was also fully human so why did God the Father accept a human sacrifice even though it was against his law?
The sacrifice of Jesus on the Cross was in compliance with the Divine Will of since it was made in order to bring salvation to mankind. It was not offered to a pagan god! So Jesus (God) did not violate the Law of Moses.