Altering the Previous Scheme for All Remaining Time

@alas_not_me was reflecting recently on fate and free will in Middle-earth (as one does), and he mentioned this sentence which I've highlighted in bold:

[O]ne of the Eldar would have said that for all Elves and Men the shape, condition, and therefore the past and future physical development and destiny of this ‘earth’ was determined and beyond their power to change[...].  The Downfall of Númenor was ‘a miracle’ as we might say, or as they a direct action of Eru within time that altered the previous scheme for all remaining time.  (Tolkien 185)

What gripped me was the idea of a divine intervention that permanently altered the prior scheme; it reminded me immediately of this passage from Perelandra:

If he [Ransom] now failed, this world also would hereafter be redeemed. If he were not the ransom, Another would be. Yet nothing was ever repeated. Not a second crucifixion: perhaps--who knows--not even a second Incarnation . . . some act of even more appalling love, some glory of yet deeper humility. For he had seen already how the pattern grows and how from each world it sprouts into the next through some other dimension. The small external evil which Satan had done in Malacandra was only as a line: the deeper evil he had done in Earth was as a square: if Venus fell, her evil would be a cube--her Redemption beyond conceiving. Yet redeemed she would be.  (Lewis 126)

Tolkien seems to be describing a divine intervention, in response to human sin, that resulted in a permanent change in the physical nature or essence of Middle-earth itself (as I recall, the straight way to the Blessed Realm was bent, so that humans could no longer get there or even see it, no matter how far they sailed).  This cutting-off of mortals could potentially be seen either as a punishment or as a means of physically enforcing a prohibition or quarantine (since mortals don't always do well with willed obedience or compliance).  Or both.  But it does not appear to be a redemptive act.

Ransom's reflections in Perelandra seem to me almost the flip side of Tolkien's comment.  Lewis is focusing on the ever-increasing evil, to which Maleldil will respond in what can only be increasingly scheme-altering ways.  Of course, Lewis is not looking at changes to the physical make-up or structure of the world, but the enormity of the divine interventions necessary to redeem fallen hnau in different worlds.

Sources

Lewis, C. S. Perelandra. 1st Scribner Classics ed, Scribner Classics, 1996.

Tolkien, J. R. R. “Fate and Free Will,” edited by Carl Hostetter. Tolkien Studies, vol. VI, 2009, pp. 183–88.