Originally Posted by
vancouver25k
Not sure if you mean using eUps or the LT-FP benefit of comp ops:
A strategy people use is to book the flight you want in advance, and confirm your eUp at time of booking (LT should clear right away when R>0, and sometimes when R=0). At T-48h, if there is J space, cancel the eUp and apply the comp-up.
I am afraid you cannot cancel the eup after it is already confirmed. You have to cancel the ticket and rebook or call in to downgrade yourself.
If you do the former, please make sure there is Y ticket available for your flight. I would always do the latter if just to be safe. And it may not be safe if J = 1, but at least you will not be squeezed out of the flight.