The multiverse theory of reality, as I understand it, is that there are an infinite number of possible universes. Further, the Universal Now suggests that all realities are happening concurrently in one "now." Hence, time travel into the future is as doable as going into the past, as they are both different aspects of now. As a result, there are an infinite number of "you," all living at once in the "now." Therefore, the notion of "past lives" and "re"-incarnation are not exactly accurate.
Personally, I believe I am changing my past and my future all the time. In fact, I consider that a manifestation of evolution. In a sense, evolution dissolves the past and the future.