I found this in another thread; it may be of help:
Originally Posted by
nigelloring
Is there a date/time change fee on DBCFREEs? (i.e. keeping routing the same, just changing date/time)
Originally Posted by
soitgoes
No, but you can't make changes to the outbound within two weeks of the outbound. Q, V, or W has to be available as well.
Since the DBCFREE books into Q, I wonder if you could call Reservations and as for a QRCARE fare LAX-SEA and use the DBCFREE as payment when you ticket it. The QRCARE allows for flexible changes to the travel, IIRC.