Can I Change the AZ for an Instance?

No.

To use a different AZ, create another instance in the desired AZ, and then migrate data and switch IP addresses. For details, see Switching DCS Instance IP Addresses.

For a master/standby instance, the AZ of its standby node can be changed by adding or deleting replicas. The AZ of an added replica can be specified. To add and delete replicas, see Modifying DCS Instance Specifications.