I had this exact problem on ANA about two years ago with the Mrs. NRT/HKG. This particular leg I was in F and she was in E. I solved the problem by simply telling the FA that she was going to sit in my chair and I in hers. They were fine with it, but it was not as easy a process as it would be on UA. On the way back PEK/NRT we decided to switch who was sitting where and such. It caused so much trouble we almost could not board in PEK. Once we got to NRT her F seat to DEN was completely gone. We were lucky that the GS agent helped us and there was a seat left in F. I would not recommend trying to fix the ticket.