You were told by Exp/THY that you can change origin and destination as well? That would be surprising to me. Normally, you change the dates and pay a change fee + any difference in fare if original booking class is no longer available. Change of destination or origin would require the ticket to be cancelled and new ticket to be booked. It sounds like you are better off by cancelling the ticket and purchasing a new ticket once you know that your travel plans are firm. Yes, you will incur a loss now but that seems unavoidable. Then you are able to move on.