1116 Schedule C Redetermination

I was wondering if anyone has had to use this new schedule. I see that there are three main areas for redetermination. You had a foreign tax refund, did not pay enough foreign tax, or the credit is still more than your U.S. tax liability.
The first two options require a 1040X for the previous year and Schedule C.
The third option requires that you send in the schedule only and original 1040? Not sure why you’d need to send a tax return back to the IRS. (I do not think the schedule can be e-filed). This seems the easiest option if HMRC tax paid for the calendar year is often more than sufficient to cover U.S. tax liability.
How does this relate to HMRC, as if you pay too much, they just lower you tax withholding via PAYE. Also, I don’t think HMRC will give a refund unless you ask/die
It used to be easy, but now more hoops.

I think the idea is that if you claim a foreign tax credit to reduce your US tax, and the foreign tax is later refunded, you need to adjust your US tax return accordingly.

I am not sure, but it seems like if you have excess foreign tax credits for that category and the refund in tax doesn’t cause your US tax to go up for the prior year, then you just file the Schedule C in the year of the refund, and you don’t need to amend the prior year.  The Schedule C for the year of the refund would reduce the amount of the foreign tax credits being carried forward into the year.

On the other hand, if the adjustment from the refund would make it so your US tax increased in the prior year, you need to amend and pay the additional US tax for that year.