In music, there are certain things considered to be under the control of the conductor's "artistic license" (exact performance tempo, dynamics, and variations thereof such as rubatos). Other things must technically remain unchanged; you can't make small changes to lyrics, for example.
Background: Say there is a single concert piece for a capella choir. Its length as written is beyond the needed time frame, and simply speeding it up to make it fit isn't an option (it's neither technically possible nor allowed by good artistic sense). However, there is a point in the piece that is a natural stopping point; the conductor could simply lower his hands from the fermata and the casual audience would consider the piece complete. This point is not a written break that would normally be considered to define a "movement" or other severable part of the piece. The piece would be performed exactly as written and instructed in the composer notes until this point.
The question: Is this legal from a copyright perspective?