The Old Testament (Moses or Jewish Bible) is IMMUTABLE Way Before Jesus Came to the Scene!

Nothing in the Old Testament may change, be adjusted, be removed, be added to: yesterday, today, and tomorrow.

Deuteronomy 4:1-2 LITV
(1) And now, Israel, listen to the statutes and to the judgments which I am teaching you to do, so that you may live and go in, and possess the land which Jehovah the God of your fathers is giving to you. (2) You shall not add to the Word which I command you, nor take from it, to keep the commandments of Jehovah your God which I command you.

Deuteronomy 5:32-33 LITV
(32) And you shall be careful to do as Jehovah your God has commanded you; you shall not turn aside to the right or left. (33) You shall walk in all the ways which Jehovah your God has commanded you, so that you may live, and that good may be to you, and you may prolong your days in the land which you will possess.

Deuteronomy 28:14 LITV
(14) And you shall not turn away from all the Words which I am commanding you today, right or left, to go after other gods, to serve them.

Joshua 1:7 LITV
(7) Only be strong and very brave, so that you may take heed to do according to all the Law which Moses My servant commanded you. Do not turn from it to the right or to the left, that you may act wisely wherever you go.

Psalms 119:89 LITV
(89) LAMED: Your Word is settled in Heaven forever, O Jehovah.

From the reading of the principle of the immutable rigor of the commandments of YAHWEH (who is Jesus, per John 14:15, because Jesus speaks of His commandments as YHWH speaks of in the above verses), the phrase 'Old Testament' is not a good choice of words to refer to the body of writings in it.

The Immutable Foundation of the Old Testament (Moses or Jewish Bible) is still maintained. EVEN WITH JESUS!

JESUS maintains that His Words in the Old Testament can never change

But it is easier for the heaven and the earth to pass away than one point of the Law to fail. Luke 16:17 LITV

The heaven and the earth will pass away, but My Words will not pass away, never! Luke 21:33 LITV

Truly I say to you, Until the heaven and the earth pass away, in no way shall one iota or one point pass away from the Law until all comes to pass. Matthew 5:18 LITV

If you love Me [JESUS], keep My commandments. John 14:15 LITV

If it is easier for the heaven and the earth to pass away than one point of the Law to fail,

Therefore, NO HUMAN BEING, WHOSOEVER, MAY CHANGE THE WORD OF GOD or TEACH or PREACH A CHANGE IN IT.

Do not think that I came to annul [LOOSEN, per the original Greek] the Law or the Prophets; I did not come to annul, but to FULFILL. Matthew 5:17 LITV

ONLY YAHWEH GOD CAN MAKE ADJUSTMENTS - NOT CHANGES - TO HIS WORD! Mat 5:17.

How would you know that someone is teaching or preaching a change or an adjustment to the word of the Messiah or the Christ?

A thorough knowledge and understanding of the Old Testament is required to know that someone is out to mislead people. If you know the foundation that the word of Jesus is the same forever, unless that word was fulfilled or was an expressed adjustment to His word by none other than Jesus, it is not an impossible task. The person has to find the text. The text will be read. Is the text about faith, behavior, or a shadow of things in Israel or at the Temple that the body of the Messiah was to suffer (Colossians 2:16)? A text about behavior and faith can never be changed or adjusted in Moses, except by Jesus. If Moses does not disagree with a behavior or a faith, the behavior or the the faith is permissible and immutable. If Moses disagrees with the behavior or the faith, the behavior or the faith is not to be followed. Note that any author in the New Testament who appears to loosen Moses (Matthew 5:17) never got loosed himself to do the loosening he appears to advocate against the stand of Matthew 5:17.
Moses does not call for the criminalization of any forbidden behavior or faith outside of Israel. Today, Jesus has not either called for the criminalization of any Bible lawlessness. He keeps knocking on the door of every heart (Revelation 3:20) and waiting for an invitation.
Faith is what the Messiah or Christ in English (John 4:25) tells us to do and to believe in order to be saved (John 3:16), without turning to the left or to the right, without adding or discarding anything. We must overcome falsehood in any of its form to sit with Jesus on His throne (Revelation 3:21).

When Moses or Jesus says 'do', we do. When Moses or Jesus says 'do not', we do not. We may not turn to the left or to the right, may not add or discard or dismiss a 'do' or a 'do not', using any rhetoric, no matter how plausible the rhetoric may sound! That is how Satan dealt and still does with man: do not do the 'do', do the 'do not'.