Let’s make this real simple....
Is Jehovah the same in the OT and NT?
Yes or no are the only two options.
My problem with the way you phrase the question is it’s as if we can change who God is by what we believe.
God does not change; the God who said to Moses in Exodus 3:14, “I AM who I AM,” is the same God who said to the Jews in John 8:58, “before Abraham came to be, I AM.”
Jews, Christians, and Moslems all believe in the same God of Moses and Isaac and Jacob. The difference is in who we believe God is.
Jews believe that God has not yet sent the Messiah.
Christians believe that the Messiah has come in the person of Jesus, and with the Father and Holy Spirit form the trinity.
Moslems believe that God revealed himself through the prophet Mohammad.
It is the same God; what we believe is not the same.
Peace,
Rich