Can one truly regret an event but not its consequences? I have in mind the sorts of events long past which were very unpleasant at the time, but about which one might say "they made me who I am today". If you do not regret who you are, can you really regret what made you who you are? Perhaps the most it would make sense to admit is a sort of prima facie regret: "Considered in isolation, that event was most regrettable. But all things considered, I wouldn't wish to alter history."
Consider Parfit's case of the 14 yr old mother. If the child grows up to have a life well worth living, albeit less good than the lives of children with more mature parents, can he rationally regret his mother's decision to have a child so young? He might wish to have been born to more mature parents, but that is not a real possibility. The only alternative is not to have been born at all. And he would not wish for that. So he must be pleased - or at least accepting - of his mother's decision. It was still the wrong decision, for reasons discussed in the linked post. But this attitude might make it easier for the child to live with. He was not harmed by the wrong, after all.
Similarly in the general case, the holistic approach to regret might make it easier to overcome our regrets, which seems like a good thing. You can come to accept past pains in the recognition that, all things considered, you weren't harmed by it. Perhaps your counterpart would have had a better life than you, in which case the past event was impartially bad. It lead to a life less good than some alternative life would have been. But it wouldn't have been your life. So the alternative would not have benefitted you. It would have made you someone else.*
* = (That incoherent claim is metaphorical of course - we cannot violate the law of identity. Really we should say that it would have made someone else exist in your place.)
A curious consequence of this view is that it also makes it harder to regret past injustices. If it weren't for slavery and the Holocaust, let us suppose, we would never have existed. Perhaps if we are very altruistic, we might regret this outcome all the same. But most of us, presumably, are not so altruistic. So we will not regret these events, except in the 'prima facie' sense. Of course, this shouldn't stop us from recognizing that such injustices were nevertheless wrong, and seeking to rectify them and/or prevent such things from re-occurring in future. Still, there's a (very loose!) sense in which you kind of owe Hitler. Doesn't that suck?