Jesus' life was transferred from the spirit realm in Heaven to the womb of the virgin girl, Mary. What is Jesus' name in the Heavenly Realm before he was given the name, Jesus, while on earth?
Attempting to identify one specific name that applied to the manifestation of God that became known as "Jesus" during its time on Earth before and after that time on Earth is an impossible quest.
John identifies Jesus as being "the Word," explaining that "the Word was with God, and the Word was God." (John 1:1) Later, John refers to Jesus as "God the One and Only, who is at the Father's side" and says that "no one has ever seen God but God the One and Only." (John 1:18)
Human intellect cannot comprehend how God could be divided into a part that remained in Heaven while another part lived on Earth. Indeed, Jesus was not completely separated from God. Jesus told His disciples, "Believe me when I say that I am in the Father and the Father is in me." (John 14:11) Later, as Jesus was praying, He addressed God when He said, "Father, just as you are in me and I am in you." (John 17:21)
There is a unity between God, Jesus, and the Holy Spirit that is beyond human understanding. They are three separate types of power or function, but all are part of the same eternal power. It is a mystery that cannot be explained rationally - it must be accepted on faith and believed based on that faith.