As stated in post #2

I'm no expert on this, but I'm pretty certain that most airlines operate same-day changes - where available - in a manner that requires you to actually request the change on the actual day of travel; it's not that the system allows you to confirm your change of flight nicely and easily well ahead of time (even a day ahead of time).

If you could process changes in this manner online by yourself ahead of time, you could always just book the cheapest flight on the day you want to travel, and then immediately switch your flight for free to the most expensive flight of the day (which is the one you wanted all along).

Same day changes are not a way for you to "defeat" the revenue department's algorithms; instead, it's a way of helping out a traveller whose meeting finishes early (or runs late), for example.

Now, whether and if the check-in staff at an outstation - where they are third party agency staff - will be able, willing, or even trained to make such a change - I genuinely don't know. I think I've read reports here - maybe even in this thread - of outright refusals and blank stares when requested at outstations. In other words, I think you might find having such a request granted is easier when you're dealing with EI check-in staff in DUB, rather than in most outstations. And I assume the same-day change also does not guarantee you a seat in Aer Space - you may end up several rows back (I expect you would still get the AerSpace Tier Credits, even though you don't get the AerSpace onboard experience, but that you would not be due any kind of refund, since it was a voluntary decision to switch, and your guaranteed AerSpace seat is still available for you on the flight for which you actually booked)

But please do report back if you decide to chance it tomorrow and head to the airport in time for the earlier flight!!!!

Maybe someone else with more experience will be able to chime in as to whether you could request the same-day change over the phone by actually calling EI in Dublin, for example....which might be a more appealing prospect than heading to the airport unnecessarily early on the chance of getting the change. I'm leaning towards thinking this can only be done at the airport, though....when a flight is moved to "Under Airport Control" there are some things that cannot be done centrally. They also probably want to verify that you are actually there and ready to depart, by requiring that you sort it all out at the airport on the day.