I know my situation does not match yours but here is what happens when "bookings" change within 24 hours.

I was to fly SEAIAH in P class, I got to the airport earlier than expected and rebooked with NO additional costs to me. 24 hour change rule was applied because I did NOT use that function - I bypassed it when asked if this change was within 24 hours and answered, NO. When I did the regular change reservation mode, it brought up a connection via DEN (SEA x/DEN IAH). That option was never available to me when selecting the option of YES for changes within 24 hours.

Here is what my accruals look like

• Activity detailsUA 2179 DEN - IAH
  pqf1
  pqp539
  Award Miles5,929
• Denver (DEN) - Houston(IAH)
• UA 2179 DEN-IAH D D 2179 | D Class
• Base miles: 2,695
• Bonus miles earned: 3,234
• Total miles earned: 5,929

• Activity detailsUA 757 SEA - DEN
  pqf1
  pqp415
  Award Miles4,565
• Seattle (SEA) - Denver(DEN)
  UA 757 SEA-DEN Z Z 757 | Z Class
  Base miles: 2,075
  Bonus miles earned: 2,490
  Total miles earned: 4,565

...AND... the O/B

• Activity detailsUA 2384 IAH - SEA
  pqf1
  pqp319
  Award Miles3,509
• Houston (IAH) - Seattle(SEA)
• UA 2384 IAH-SEA P P 2384 | P Class
  Base miles: 1,595
  Bonus miles earned: 1,914
  Total miles earned: 3,509

The airfare was the exact same amount for the outbound flight and I did not have an add-collect for the return flight. Almost 300% more PQP, 300% MILES, and 200% more PQF. You can see the fare bucket class of service on the return segments are Z and D instead of P. That is the only "difference".




I poked the bear on PlusPoints - I wasn't thinking and instead of being charged 20 PP, I was charged 30. In the end.