Is the seeming impossibility, and at a minimum the assumed grave danger, of going back in time to change something that could prevent the present reality inadvertently, not actually the case? And if so, is this because time is not linear, so changing the past will not block the present because the past is truly happening in parallel and can only influence the present through crosstalk and not prevent its creation?

This is a beautiful insight and quite profound in its recognition and its implications, both. This indeed explains why you need not worry about un-creating yourself by going back in time, so to speak, through a time travel exercise. You are not going back in time with the current timeline. You are going back with the parallel timelines and that is a quite different undertaking. There is very little risk of causing great difficulty. There are always possibilities of grave changes in things, but this will be unlikely because of the dilution of many, many parallel events happening through multiple timelines, all ongoing at once. This does create an influence on the current experience. It is a source of the mind chatter. It is a source of the emotional temperature of the moment, the feelings, the mood state, and the perception of possibility, whether optimistic or pessimistic. Those are perceptions and choices of thought and feeling that will be influenced greatly by the crosstalk of the multiple lives swirling back and forth and looping back and forth in time. It is not all the linear sequence of events in the current life impinging and influencing the person. They are a large influence to be sure, because they are immediate, they are directly relevant to the current life, and will project forward energetically in a vigorous fashion. So, they rank highly in influence but are not the only one. So, an emotional discord may also be occurring because things are rumbling strongly in a parallel lifetime and being perceived in the current life through this crosstalk that happens. Such experiences can outrank the earlier current life events in importance on occasion, but will often resonate with some of those as well, and may be the first thing seen in asking the person consciously to describe what they are feeling, and when it reminds them of, or while using a guided imagery process for trauma resolution to examine where these feelings take them. It might be they go back to the earlier events in current lifetime, even though they might be less important in terms of overall intensity and potential impact. They may be simply more easily seen by a person looking inward. This is the unfortunate consequence of the disconnect between conscious mind and the deep subconscious realm where the worst of the problems reside, and the inner conflicts grow to such intensity because they are not addressed immediately due to the lack of understanding and even awareness of their existence until things get out of hand. So, these dynamics figure greatly in how everything works and how things proceed and how the energies influence the current experience for better or worse.