You can get the record locator number and list yourself on Travelnet as soon as you get assigned the DH flight. You have to wait until 24 hours prior to departure to change your seat assignmnent. It's not a perfect system yet. I've tried changing my seat on the internet and it says there are no available seats when Travelnet shows 20+ open. Then I get to the airport and the kiosk will have a few seats to change into, and then you get to the agent and they have lots of options. I'm not sure how they release the seats into the kiosk system and the internet system so you can change them yourself, but they very rarely match. It's still a better way to try and get a better seat than begging the agent.