I'd like to make sure I'm reading the rules correctly.

Same day changes have limiited flexibility to get you on departures the previous calender day: if you're originally flying SEA-ANC at 1230AM on Monday, you could SDC to the Sunday 1030PM departure. You cannot do the reverse and switch to a flight on the following calender day, correct?

I have an afternoon FAI to SEA and a change of plans makes the following morning's (130AM) departure more convenient. I believe this would require a refare as it's on the following calendar day. Seems like an exception a la the "after 10PM previous day" would make sense for early morning red-eyes.

Leaving after 5pm, but before midnight would require a change of routing in my case, so I don't think that's an option without refaring to the walk-up Y rate.