Faith in Jesus Christ does not take away the faithfulness of Christ going to the cross. (Romans 3:24-28) It's not about changing "OF" to "IN" as if "OF" is the concrete interpretation and "IN" is in error as if it changes Galatians 2:16 to mean something entirely different.
In Galatians 3:26 in the KJV, we read - For ye are all the children of God by faith in Christ Jesus.
In Ephesians 1:15 in the KJV, we read - Wherefore I also, after I heard of your faith in the Lord Jesus, and love unto all the saints.
In Colossians 1:4 in the KJV, we read - Since we heard of your faith in Christ Jesus, and of the love which ye have to all the saints.
In 1 Timothy 1:14 in the KJV, we read - And the grace of our Lord was exceeding abundant with faith and love which is in Christ Jesus.
In 2 Timothy 1:13 in the KJV, we read - Hold fast the form of sound words, which thou hast heard of me, in faith and love which is in Christ Jesus.
In 2 Timothy 3:15 in the KJV, we read - And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus.
In Galatians 3:26 in the KJV, we read - For ye are all the children of God by faith in Christ Jesus.
In Ephesians 1:15 in the KJV, we read - Wherefore I also, after I heard of your faith in the Lord Jesus, and love unto all the saints.
In Colossians 1:4 in the KJV, we read - Since we heard of your faith in Christ Jesus, and of the love which ye have to all the saints.
In 1 Timothy 1:14 in the KJV, we read - And the grace of our Lord was exceeding abundant with faith and love which is in Christ Jesus.
In 2 Timothy 1:13 in the KJV, we read - Hold fast the form of sound words, which thou hast heard of me, in faith and love which is in Christ Jesus.
In 2 Timothy 3:15 in the KJV, we read - And that from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus.