So first let me say I realize this is my fault, not NH's. I know I am responsible for getting my own visas and documents in order. I've had many visas to this country, and was not expecting trouble, but was denied in this case. So I realize my error is the cause here.

That being said, I'm a little confused on this one, despite quite a bit of flying experience. NH ticket stock, but no NH operated flights, only a code share (I believe) on the longest leg NRT-LAX. Operating carriers are UA/UA/HX/VN/UA/AS. Purchased on Priceline for a last minute ticket a few days ago. I believe Priceline will not be helpful, but will call soon and make an attempt. My sense and quick research leads me to think asking NH for cancel/change might be my best hope here since it's their stock. So a few questions, if anyone is so kind.

First, departure is 27 hours from now. Do I need to change things before departure? Before 24 hours of departure? Before date of departure (21 hours from now)?
Second, I'm assuming my strategy should be try for cancel and refund, but if not allowed as assumed, try for a change. But is that then only a date change, or can I do a change of departure/arrival locations? I don't have fare rules in front of me, so I apologize for that also.
Third, I haven't had to deal with IRROPS much, but I know with award travel I've heard/seen discussed that leading up to departure a ticket goes from booking airline control to operating airline control (my terminology might not be the best with that). Is there a point where UA will replace NH as having control over this ticket and I'll have to contact them?

Thanks for any thoughts.