I tend to think that Heidegger (early, anyway) may be closer to W and Gadamer on the flexibility of background practices than you suggest. This was a claim in my diss (that he’s closer to G). The basis of my argument turns on authenticity. Ted frequently pointed out that Heidegger is clear that an authentic Dasein’s world need not change. But I believe an interpretation that couples sections 61-63 with chapter 5 yields a position in which the tradition which we inherit can be modified by us. The specific direction such modification takes is, of course, not directly guided by the subject — it happens, as you say about W and G, in the absence of rules or princples. I think Heidegger’s account of fate, in other words, is one in which Dasein is a full participant. And only authentic Dasein, as Heidegger stresses, actually has a fate.