if it's the first piece switch that makes it no longer the same, then anytime you fix physical, it's not the "same" anymore. this keeps me up sometimes. please help
it's like a gradient. you can speak about it on any level of detail. maximum level of detail would specify exactly how much, and which parts, have changed. minimum level of detail would either call it a new ship or the same ship, depending on whether the conceptual identity or physical condition is the subject of the conversation