I recently moved a female passenger (to club as it was the only spare seat) who I and the other crew could see was distressed by being blocked in by a large passenger. She was very grateful. This was not in an exit row. If it had been an exit row, I would have been required to move the large passenger and swop him with someone else.
If someone is disabled, frail and elderly, obese or a child, they cannot sit in an overwing exit row and the cabin crew will move them.
(All my opinions are my own personal opinions and I do not speak for or on behalf of British Airways)