Originally Posted by Apieinthesky

Yes. If there is F availability on the long haul segment, I would confirm it now. If there is Y sAAver availability, you can take a voluntary downgrade. Then, if F availability opens up later (or on a different DFW-LAX flight), you may upgrade or switch for no fee. Changing the dates or routing without changing O/D will incur no fee.

If you are still in Y on that domestic segment on the day of the flight, you should be above Y>F upgraders on the airport list.