I had a car with a TPMS fitted and had no problems with replacing the tyres. They are part of the valve assembly (they looked like aluminium blocks on the inside part of the valve) and you don't replace them. Let your tyre fitter know they’re fitted as they can get damaged when he takes the tyre off and he has to put the wheel back on the same corner it came from, otherwise you have to retrain the system.
It doesn’t matter what size tyre you refit, as long as the pressures are going to be about the same, as they work by detecting pressure in the tyre.
Look at your bill at the end to make sure they haven’t charged you for new valves.
