I once swapped an aisle seat at the back of the plane for an aisle seat halfway to the front, but otherwise identical so that two related people could sit together. This was an DC to Stockholm trip so not exactly a couple of hours on a midcon.
Only problem was that the person who was in the middle seat came along a few minutes after I had settled into my new seat, and he was huge, easily 300lbs. The cabin attendant could see my discomfort and plied me with free drinks for the duration of the flight.... after that I decided that unless I could see me new seatmate and 'size them up' it would be a thanks but no thanks.