Metabole (meta-ballein) means first of all "to throw away" in ancient greek. And Geworfen in german means the same thing.
Texts in Beiträge show that the later Heidegger was focused on the same central topic as the earlier: the a priori openedness of the open-that-gives-being.
In the early period this openedness of the open was termed Geworfenheit, whereas in the later period it is called Ereignetsein. Thus Beiträge equates geworfen with ereignet (GA 65, 239.5 and 304.8) and with zugehörig der Er-eignung (252.24), and it reformulates die Übernahme der Geworfenheit as die Über-nahme der Er-eignung, without changing
the issue (GA 65, 322.7 and 327.7; cf. GA 2, 431.13).
What Heidegger is expressing in both the earlier language of Geworfenheit and the later language of Ereignis is that being-open is the ineluctable condition of our essence, not an occasional accomplishment of our wills.
It is our "fate," the way we always already are (GA 2, 431.16-17). This is the central issue of his thought, and it does not change between Heidegger I and Heidegger II. To-be-the-open is to be a priori opened, and only as such can we take-things-as. Dasein is "erschließend erschlossenes" (GA 27, 135.13), able to open up other things only because it itself is already opened up.
That is why we should not translate Dasein as "being-there" or "being-the-there" or "there-being but, rather, as "always-being-open" or "already-having-been-opened," or "apriori openedness." But those phrases are so immensely awkward, and as Richardson says, "a man must live with himself" (579, n. 6).
So we can settle simply for "openness."
