Originally Posted by
Often1
This is not correct, presuming that OP is on a non-refundable/changeable ticket. When OP cancels, the entire value of his ticket will be a credit. He will then need to pay $150 in new money in order to access the credit. Depending on the value of the original ticket and the cost of the new ticket, this may or may not make a difference.
Before going through all of this, it is worth pricing out a new OW LAX-SEA. Sometimes its worth just letting the original RT go.
But, just skipping the first segment is not an option.
OP - when is your travel date? OW ticket for SEA-LAX can go as low as $113 so might not be worth it to pay the change fee and all of that. You may be able to talk your way into just having them waive the change fee and just keep your ticket without getting any refunds or just get a new OW ticket.