Can retrospective past actions change a future that has already happened?

All I can say is that this question arises from another discussion about the ethics of time travel. In an answer, I found myself writing this, and I looked at it, and it twisted me into about seven different dimensions. Kind of mind warping.

So I thought I’d let you all try to make sense out of it. You can look at it from a range of perspectives, but I will suggest two. First, let’s answer it from a perspective where our reality would make it possible for this to be a sensible question. Second, let’s look at it as a metaphor that allows us to deal with something in our current reality. What is that something?