There are many types of "round the world" ticket. Clearly this is a rtw ticket in some sense since you are going round the world. The question is whether it is a OneWorld Explorer ticket (as you were apparently led to believe) or something different entirely (as I suspect).

I believe the change fee will get converted from USD at some not very good exchange rate, but I could be wrong about that.

I still reckon your best bet may be just to fly back to HNL the evening before. That way you don't have to open the whole can of worms with the ticket. But I would make very sure you have some solid documentation for what you've bought.