Normally we might have an intuition that personality has thickness and substance. For example, if some spiritual entity were to possess my body, I would ordinarily think that I should become displaced. Why? Because personalities are thought to collide and contend with one another, similarly to how billiard balls do. Similarly to how two billiard balls cannot occupy the same space, we often imagine that similar properties apply to personality. So in this way of thinking, only I can be myself, and only I can occupy this human body, and so on. Also from this way of thinking I have only one past, and I will have one continuation in the form of one other personality occurring in the dream after this big dream ends (rebirth after the death of the body).
However, consider for a moment the implication of everything being just mind. It means no phenomenon, including personality, has any kind of substance or thickness, and so nothing needs to contend with anything else for one.
So imagine this scenario. I am standing here. And opposite of me TriumphantGeorge is standing. Now TriumphantGeorge mentally possesses my body, and what happens? From my POV I may go on just fine. From TG's POV he may also go on just fine as me. There is no collision. There is no displacement happening.
In fact, in this very moment, just how many Nefandis live in this very body? Conventional answer is one. However, potentially countless Nefandis live here right now. As well countless beings live here who have possessed this body. Since none of this has any thickness, we can fit here just fine, and there is no contention at all.
Another implication is the possibility of having multiple concurrent pasts.
So if me and TG become the same being in the next rebirth, that being's past will involve parallel pasts of me and TG. Since my present past can also involve parallel pasts, it's possible that the past can be infinitely parallel even though it seems to lead to a single unified present moment.
Going forward the same thing can happen. What was one being here, like say Nefandi is one being now, becomes 100 beings in 100 different rebirths. Each of those 100 beings remembers his, hers, or its past as this Nefandi right here, while they are quite distinct and quite separate in the future.
So there is not necessarily a "preservation of energy" happening because there is no substance. So one personality can become many. Many can become one. Such transformations would be impossible, and would make no sense, in the view of substance. But because in the mind nothing can have substance in the ultimate sense, some extremely weird happenings are possible.
So when you hear 10 New Agers all claim to have Cleopatra as one of their past lives, maybe this time you won't laugh at it. You'll know, actually, this is entirely possible and is consistent with the view of personality not being anything substantial.
That said, there is a huge difference between personality and you. There is always one and only one you. It's important not to become confused here. You aren't the same thing as a personality. You're a capacity to experience, to know, and to will. Any specific personality is just a peculiar way to exercise that capacity. And because the capacity is limitless, it can conceive of and exercise some exceptionally peculiar personalities, such as a personality with 5 concurrent and parallel past lives, for example, or being a brother in a family of siblings, all of whom without exception are a rebirth of a single being, which is to say, all of them remember the exact same events as their past.
Because past and future are merely narratives, they can be anything whatsoever. Narratives have no thickness and they're not obliged to follow any laws. There is no law of conservation of narrative in the mind. The mind can commit to such a restriction for a time, but it wouldn't be a law.
Also, here's a freebie. What does it mean to be reborn? It means to believe your experience. If you take your experience now at face value, it means you've been born or reborn.
However, if you believe nothing that you experience right now, and take nothing concrete at face value, then you've transcended the cycle of birth and death.
So being taken in by the visions the mind is having is literally birth and death cycle. If you're not taken in by those visions, you're literally free right now. So if you're not taken in by this post right now, you're beyond birth and death, right this moment. Then you can know yourself as the ever-dreaming mind, the mind that has no beginning or end or other parameters, the mind as a capacity.
Alright, that's enough fun for now.