Sure. These people were in covenant with God externally being called to obedience of faith, not salvation. Moses explains that the word of God has come down, they do not have to search for it, it was right there for any who obeyed.
Paul quotes from here showing in the gospel the word of God is also right before the people , preached and taught, they do not have to ascend, or look below, it is right there.
Paul talks about two covenants; the law & faith in the gospel. You have to look back to the first person saved by grace through faith in the gospel of Jesus Christ to understand when the covenant of faith was created.
Galatians 3:6-9 (NASB) 6 Even so Abraham BELIEVED GOD, AND IT WAS RECKONED TO HIM AS RIGHTEOUSNESS. 7 Therefore,
be sure that it is those who are of faith who are sons of Abraham. 8 The Scripture, foreseeing that God would justify the Gentiles by faith,
preached the gospel beforehand to Abraham, saying, "ALL THE NATIONS WILL BE BLESSED IN YOU." 9 So then
those who are of faith are blessed with Abraham, the believer.
14 in order that in Christ Jesus
the blessing of Abraham might come to the Gentiles, so
that we would receive the promise of the Spirit through faith.
16 Now the
promises were spoken to Abraham and to his seed. He does not say, "And to seeds," as referring to many, but rather to one, "And to your seed,"
that is, Christ. 17 What I am saying is this:
the Law, which came four hundred and thirty years later, does not invalidate a covenant previously ratified by God, so as to nullify the promise. 18 For if the
inheritance is based on law, it is no longer based on a promise; but
God has granted it to Abraham by means of a promise.
The Law of Moses came 430 years after God had already ratified the covenant of faith in the gospel with Abraham. This means that The Law has never existed outside of the covenant of faith, but the covenant of faith does exist outside of and apart from the Law. Paul makes the point:
Galatians 3:15 (NASB) Brethren, I speak in terms of human relations: even though it is only a man's covenant, yet when it has been ratified, no one sets it aside or adds conditions to it.
Paul is saying the covenant of faith was ratified 430 years before the law, and once ratified, you can’t add conditions to the covenant... so The Law didn’t modify the covenant of faith.
Galatians 3:26 (NASB) For you are all sons of God through faith in Christ Jesus.
Galatians 3:29 (NASB) And if you belong to Christ, then you are Abraham's descendants, heirs according to promise.
So yes, Deuteronomy 30 can and is spoken to those under the covenant of faith. All Christians are saved by becoming qualified for the blessing & covenant & oath God made with Abraham for his faith in the gospel of Christ.
Romans 4:5-13 (NASB) 5 But to the one who does not work, but believes in Him who justifies the ungodly, his faith is credited as righteousness, 6 just as David also speaks of the blessing on the man to whom God credits righteousness apart from works: 7 "BLESSED ARE THOSE WHOSE LAWLESS DEEDS HAVE BEEN FORGIVEN, AND WHOSE SINS HAVE BEEN COVERED. 8 "BLESSED IS THE MAN WHOSE SIN THE LORD WILL NOT TAKE INTO ACCOUNT." 9
Is this blessing then on the circumcised, or on the uncircumcised also? For we say, "FAITH WAS CREDITED TO ABRAHAM AS RIGHTEOUSNESS." 10 How then was it credited? While he was circumcised, or uncircumcised?
Not while circumcised, but while uncircumcised; 11 and
he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be
the father of all who believe without being circumcised, that righteousness might be credited to them, 12 and the father of circumcision to those who not only are of the circumcision, but
who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. 13 For
the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith.
Ephesians 1:13-14 (NASB) 13 In Him, you also,
after listening to the message of truth, the gospel of your salvation--
having also believed, you were
sealed in Him with the Holy Spirit of promise, 14 who is
given as a pledge of our inheritance, with a view to the redemption of God's own possession, to the praise of His glory.
The Holy Spirit’s indwelling is “circumcision of the heart.”
Romans 2:29 (NASB)
But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter; and his praise is not from men, but from God.
Colossians 2:11 (NASB)
and in Him you were also circumcised with a circumcision made without hands, in the removal of the body of the flesh by the circumcision of Christ;
What is the context of Deuteronomy 30?
Deuteronomy 30:6 (NASB) "Moreover the LORD your God will circumcise your heart and the heart of your descendants, to love the LORD your God with all your heart and with all your soul, so that you may live.
So I disagree with your assessment that Deuteronomy 30 is about the covenant of The Law. Certainly it is in regards to the very covenant of faith by which we are all qualified to be in Christ.