Does this question relate to one loan, or are you writing a policy/procedure?
Assuming that you are trying to decide how to disclose a single loan,
1. is this loan a workout?
2. before or after the changes you are making, did/will this loan have a variable interest rate?
If your answers to these two questions are "no", then you are only concerned with the general rule, not the exceptions. The general rule hinges on the way your state law views the changes you are making to the legal obligation between the bank and this borrower.
What's most important is not what you're changing, but how you're doing it. If the borrower will sign a whole new set of the same documents that created the loan and then you mark the old documents "paid", "cancelled", or in some other way that renders them irrelevant in the eyes of a state court, then you have what Reg. Z declares to be a "refinancing."
More likely, you are not voiding the old credit documents in their entirety and it will not be necessary to refile the deed of trust. Instead, the borrower will sign a supplemental agreement that says (more or less) that all the original terms of the loan remain in force without interruption, except for the one, two, or several terms that will change. It doesn't matter whether these changes are drastic. You could, for example, extend the term from 30 days to 30 years, increase the interest rate from 2% to 200%, or change the monthly payments by a tiny fraction to a large multiple of the previous payment amount. As long as the changes are surgical, you are simply modifying the old contract and Reg. Z does not call it a "refinancing."
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...gone fishing.