I was booked and confirmed on MNL-SIN-GRU round trip award flight in few months from now. Want to change the to the later flight (for shorter connection in SIN but was told that even it shows available (when looking as single sector MNL-SIN), for my iterinary its not available but on waitlist due to married segment concept since the connecting SIN-GRU is on waitlist as well even though Im confirmed on that flight?

I plan to do a stopover in SIN (which is basically free since Im on roundtrip saver award), so , If I take the MNL-SIN two days before, will the married segment still applicable? Will the computer still says that the connecting segment though leaves 2 days later is still on waitlist (though in my case, I'm confirmed on connecting SIN-GRU leg?

So a married segment ticket from X to Z with a stopover in Y, to change a date on X to Y, will the computer looks for availability of X to Z or just the X to Y?