Since I wrote this piece it has become clear that the EU is not in the business of re-opening the Agreement at all. They have also moved away from offering more formal reassurances which seemed to be on offer in draft. Instead more of them saying the disagreement between the Commons and the Prime Minister on the Agreement is another reason to need the backstop insurance. The Prime Minister has changed her language back to reassurances from legal changes.
It is difficult to see the DUP coming back on b0ard given the lack of any legal text to remove the backstop. Were there to be a change of heart by the EU in the new year on this matter, there are still considerably more Conservative MPs than the government majority with the DUP who oppose the Agreement for a wide range of reasons including sending them too much money, delaying our exit without a clear end date, and putting us under EU rules for an indeterminate period with no vote or voice on what new burdens and requirements they might impose.