From the WCF 21.1, ...But the acceptable way of worshipping the true God is instituted by himself, and so limited by his own revealed will, that he may not be worshipped according to the imaginations and devices of men, or the suggestions of Satan, under any visible representation or any other way not prescribed in the holy Scripture.
Frame does not deviate from the accepted and applied understanding of the confession here at 21.1. Where he would differ in understanding is in 1.6 as it would apply to 21.1. 1.6 states, ... there are some circumstances concerning the worship of God, and the government of the Church, common to human actions and societies, which are to be ordered by the light of nature and Christian prudence, according to the general rules of the Word, which are always to be observed. Here there is not even agreement of past or current adherents to the confession of the definition of "circumstances." Regardless, these decisions should still be made to the Glory of God. Further he writes concerning this, ...the term best suited to describe the sphere of human judgment is not "circumstance," but "application" (pg. 41, Worship In Spirit and Truth). Applications would include issues such as Scripture instructing us to pray, but does tell us what words to pray. Scripture instructs us to meet, but not when or where. We must us our best judgment in these issues. So, some issues are and some are not common to human actions and societies. Hence, the RP for worship applies here as well. This does not give us carte blanche to do as we please in worship. We must exercise godly judgment. We must, however, recognize that Scripture draws distinctions in different situations. Such as, to use Frame's examples again, the Lord's Supper is not an common meal, if some are hungry let them eat at home, not at the worship service. He advocates that in the decision making process that we are always subject to Scripture whether about worship or any other sphere of life. Lastly, he adds, Human wisdom may never presume to add to its [Scripture] commands. The only job of human wisdom is to apply those commands to specific situations.
Carrying this into the realm of music, Scripture does not in my opinion, based again on 1 Cor. 14, define what we are to sing. Often, I believe we should sing the Psalms or other portions of the Bible, but that's based on pragmatic reasons rather than biblical. It would be great to sing the Psalms to modern music. Frame in his book Contemporary Worship Music expertly lays out his position on this.
Returning to the first principle, he rightfully claims on page 67 of WISAT, ...Scripture also tells us, and more explicitly and emphatically, that worship should be intelligible. It should be understandable, to the worshipers, and even to non-Christian visitors (1 Cor. 14, especially vv. 24-25). And intelligibility requires contemporaneity. When churches use archaic language and follow practices that are little understood today, they compromise that biblical principle.
I hope I have accurately portrayed Frame's views here. To be sure, buy the book, give it a read and let's explore this area of RP and CWM.