I've been thinking about it... and I've found a way how it seems to be possible.
Because, I like the idea as well, and although it logically didn't make sense it did feel right... so I kept thinking about it and I think I have a solutions
When we are incarnated we are always in the present. There is no future yet.
When we want to incarnate in the past, we cannot do that in the same dimension because it already happened. There was already somebody else this person.
So, what happens is that we create a new Dimension where the time we incarnate in, is the present. The future that we have already lived, in the other dimension, has not yet happened there.
This includes free will. For example, if I want to incarnate as Cleopatra I could do that, without messing with history as we know it. I might not become farao or I might die at age 15... but the history as we know it in this present will still be the same because it will have happened in a new dimension.
Everything before Cleopatra will have been the same (in order to create the same circumstances as in this dimension), but from that moment of birth on, the dimensions will split.
And this could happen for everybody all the time..
That is cool!!!
It actually also makes sense in conjunction to my other believe, that we are all part of 1 powerful being. Why would 1 being only want to play with one person? With one or even a few life times? If they are all powerful they would want to be all of us, in every possible variation. So, creating multi dimensions makes sense from that point of view as well...
Cool... the universe makes a bit more sense again..