I want to make sure we are clear here. If you purchase NOW and change the outbound part of the ticket, it's not a change fee. You gotta buy a new ticket with credit left from the other ticket minus the $150 ASC.

Now, if you buy one NOW for say Jan 22nd and travel on that date and pick some date about 10 days later to return...you can change the return for only the $150 plus any fare increase BUT as long as the fare bucket is open (regardless of advance purchase requirements) then you only owe the $150. With some flexibility, you ought to be able to find something within that same fare class.