...and how would you actually do that if we assume that your travel has added matter to the universe, rather than completed an iteration of a time loop that was happening there already?
Yeah, "interfering with" is open to interpretation. One might argue that you don't have to say "hi" to yourself to interfere with, and it is sufficient to be within the same light cone.
...and how would you actually do that if we assume that your travel has added matter to the universe, rather than completed an iteration of a time loop that was happening there already?