This is a difficult question to answer. We are told pretty consistently that time does not exist and that all our earth-lives (and all of earth-time) are happening at once, with our lifetimes actually influencing one another. So in theory, yes, you could mix up your incarnations out of order that way. But a great deal would depend on why you would want to do that! If it's just because you want to wear love-beads and try LSD, then such a lifetime likely would not be approved and you wouldn't be able to locate a body being born there. But if, on the other hand, you had a specific set of experiences that you and your primary guide thought were important for you to have for your own spiritual growth, and if a body that could be used to have those experiences was about to be born in 1969, then you might well be offered that body. So it's hard to say!