Forget "Jehovah" -- it was the Latinization of the much older Yehweh (YHVH), which is thought to have come from the Canaanites or the Egyptians. Actually, the name, which is believed to mean "He Commands the Wind, or Storm," actually was given by God to Abraham who then subsequently lived among the Egyptians and taught them astronomy and mathematics. The name, as given, was "I Am," which was also given to Moses. The name itself was also, in later form, said to mean "the Unchangeable One." Exodus 6:3 says that He was known to the earliest patriarchs as El Shaddai (God Almighty), but by the name Jehovah was He not known to them. This is contradicted in other writings and has led some to wonder if the original text wasn't posed as a question (there have been numerous changes over the centuries, but none containing huge doctrinal problems).
The biblical text does not say where the various forms of God came from, but we know the patriarchs respected the name and refused to say it, substituting the word "Lord" for it. I'm not sure where you got the "changeable" part of the name as it was just the opposite. Technically, the early Christians saw YHVH as being Christ, the Mediator, not the Father. If you look at the titles, the role, everything -- the Son is the one who spoke to Moses. He was God of Israel and the Judge of mankind (see Margaret Barker's The Great Angel: The Story of Israel's Second God**). She argues that the earliest Hebrews saw Yahweh as God's Son, not the Father.
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**What did "Son of God," "Messiah," and "Lord," mean to the first Christians when they used these words to describe their beliefs about Jesus? In this book Margaret Barker explores the possibility that, in the expectations and traditions of first-century Palestine, these titles belonged together, and that the first Christians fit Jesus' identity into an existing pattern of belief. She claims that pre-Christian Judaism was not monotheistic and that the roots of Christian Trinitarian theology lie in a pre-Christian Palestinian belief about angels--a belief derived from the ancient religion of Israel, in which there was a "High God" and several "Sons of God." Yahweh was a son of God, manifested on earth in human form as an angel or in the Davidic King. Jesus was a manifestation of Yahweh, and was acknowledged as Son of God, Messiah, and Lord. Barker relies on canonical and deutero-canonical works and literature from Qumran and rabbinic sources to present her thoughtful investigation.