Movement Question

I am fairly new to this game and never posted on the forum. I cannot find the answer to this movement question and I was hoping to have someone clear it up. I noticed while making certain troop movements, I can go back and cancel them while some they appear locked. Can someone tell me when it is determined a move is final and when it can be cancelled?

Also, if you make a move and then cancel it, does it effect the priority?

Thanks in advance..

I don't know about the first question, but I'm pretty sure that canceled moves don't affect priority.

I don't think they affect priority.
You can cancel any move, if after that move, you don't merge to that stack / move that stack.