Instead of a performance that holds all the data for a performance, it would be nice to have a "pointer performance" that points to another existing performance.
Let's say I have four different performances for four different songs. A, B, C and D. With pointer performances I could then make setlists that contain the songs in different order, like 1: BACD and 2: DABC without copying performances to multiple locations.
Pointer performances would not need to have any specific additional "mode". Pointer performances would just need a flag to normal performance that indicates it is a pointer performance and the performance number where it points to.