Who usually owns re-validation scope after FAT/SAT changes?

For people who work on commissioned production systems: If FAT/SAT is complete and a later PLC, robot, safety, or configuration change raises the question of whether previous test evidence still applies, who normally owns deciding the re-test scope? I’m particularly interested in the responsibility side rather than the technical test procedure: - integrator/commissioning team, - customer automation, - quality/validation, - operations, - or someone else? And if there's disagreement about whether the machine is ready to run again, how is that usually resolved in practice?