Posting on behalf of a friend. He works in a fast food place and rotas are posted around a month in advance. Each week the employees work different days. There is no pattern at all so planning ahead over a month is impossible and you'd need to officially request specific days to be avoided a month in advance. Some weeks you could work 10 in a row because week one he's in Wed to Sun and in week 2 it's Mon to Friday.
Friend, Let's call him Bill, needed a specific day off and asked if a shift swap could happen. He found someone in his same role, applied for the change, filled in the paperwork with the colleague and had it approved. The rota was officially changed by the manager. Bill did the other person's shift but when his swapped shift came, the other person had called in sick. Bill was called into work and threatened with a disciplinary if he didn't because he would be classed as a no show for his own shift (which it no longer was). Bill had to cancel his plans and go to work. He's furious. Not only with the colleague but with the boss. The shift was swapped. The rota was changed. He completed the shifts he was required to. Is this right or not? Google isn't telling him anything useful.