Semper reformanda as a “slogan” is not Lutheran. Semper reformanda as an idea is Lutheran. But it does not mean what you say. Semper reformanda is to the Christian Church what a repentant life is to the Christian. Just as the individual in this life is to be continually returning to the Lord sorrowing over his sins and desiring God’s forgiveness and strengthening so that he might live before God as His true child, so too is the church on earth (which is composed of nothing but repentant children of God) to be continually returning to the foundation of the Apostles and Prophets in order to examine herself, her doctrines and her practice, to see that they are in accord with God’s revealed will.
Real Lutherans subscribe unconditionally to the Lutheran Confessions, that is, to the Book of Concord of 1580, which is composed of the three Ecumenical Creeds, the Augsburg Confession, the Apology (Defense) of the Augsburg Confession, the Small Catechism, the Large Catechism, the Smalcald Articles, the Treatise on the Power and Primacy of the Pope, and the Formula of Concord. These confessions are understood to be the “norma normata” of Christian doctrine because they are draw from that which is the “norma normans,” i.e., the only source and norm of Christian doctrine, the Holy Scriptures of the Old and New Testament. Far from being “ever changing,” this is ever returning to the doctrine that never changes.
There is no modification of the Book of Concord. Truth remains truth.