Okay peeps, here is my experience on several TP flights last month:
What we already knew:
You have to pay for a seat, even if you are *A gold. T-3 from the flight all seats are available and you can play around.
When you check-in, you get assigned to a random seat indeed but here is what you can do:
* Wait for T-3 and change your seat then
* Select a seat you would like (even exit rows or preferred seats) and then just don't pay for it. This way, as reported before, you won't be able to change back to your free selected seat (even if you cancel check-in and start over, the system will remember your seat and will ask for charge). You cannot get a boarding pass but for the system you are checked in and the payment is pending (but your seats are blocked). So then, you can wait for T-3 and then you will be able to select your (previously overcharged) seats! Amazing, huh?
Wondrous thing of this system is that it somehow even works for connecting flights: So I had a JFK-LIS-BRU flight, and I did the above trick. T-3 I was at the airport and could select all seats on JFK-LIS but not for LIS-BRU. Went at the check-in desk and agents were really puzzled around this... What they finally did, is cancel check-in and try it again on their system and as you might have guessed, the system assigned me the seat that I had already "selected" free of charge of course.
Other things to note:
* The ponte-aerea OPO-LIS in not applicable to above rules: Seat pre-selection is not available and during check-in you can select any seat. Also, you can hop on an earlier flight if you arrive at the airport.