I agree that this could be written more clearly, but I was also reading it as how
@EACarlson reads. If a reservation existed on 5/27, then then next activity (cancellation or change) would still be subject to current rules and any flight credit generated for that instance would be non-expiring. That flight has not yet been "changed on or after May 28, 2025" so the action you take on that flight is pursuant to the old rules.
If your flight dropped after 5/28, the first change you made after 5/28 would generate a a non-expiring credit, but that would mean that your ticket was now subject to the new baggage and credit rules because that's when the ticket would have been changed after the deadline.