No airline will accept No. 1. You need to go for No. 2 and pay the applicable change fee + any upfare if the booking class is no longer available/a higher booking class is needed. It may turn out to very expensive and it may be cheaper to wait buying the ticket until the return dates are fixed.

You need to familiarise yourself with the fare rules for the return flight before you book.

The costs would not be covered under any travel insurance that I know of.

I would skip Priceline or Exp. and book directly with the airline if possible - in particular if you know that you will have to change the ticket afterwards.