Ok 1. Only about 3 or 4 people have said book an appointment and I do believe a dozen is 12. Unless you mean a bakers dozen then it's 13, and I have said it hard to get appointments.Best of luck in your warranty exchange.
2 I have had a Mac exchanged for a new model and didn't know if it works the same with iPhones
And 3 yes the Belfast Victoria square store and I have gone through the app and the website and both are saying there are no appointments available.