Your question, yes to both (I opening up later and pay $25 to change award ticket), but my advice for you at the moment is booking that outbound flight with 45K miles ASAP. I'm even surprised to see those seats available this late, it's unlikely will even find cheapest revenue J at this point, let alone limited capacity I.

Returning, if possible, be flexible with dates and/or segments, have you checked IST-BOS or IST-ATL? Also TK3 is usually the easiest to find limited award in J on IST-JFK, don't limit yourself to IST-IAD.