Your first and third scenario seem not to honor conservation laws, one can probably build some nasty consequences out of that. Or what happens to the matter occupying the space you are about to appear in, where does it go? In the third scenario it can not simply switch places with the matter from the future because that would kill the asymmetry of that scenario and provide a way to send stuff to the future. I was not simply talking about you killing your younger self. To have any real merits one has to analyze a time traveling scenario with the same mathematical rigor as our normal physical theories. But I never thought much about about time travel because it is such an hypothetical idea and therefore my example a probably pretty bad but I hope you get the idea of what I am aiming at.