1. A system for restoring a secondary copy of data generated in a first storage management system to a client of a second storage management system, the system comprising: a first storage manager for managing storage operations in a first storage management system; a second storage manager for managing storage operations in a second storage management system which is mutually autonomous with the first storage management system; a first storage device component of the first storage management system comprising a secondary copy of data generated in the first storage management system; a secondary storage computing device comprising a media agent component of the first storage management system, wherein the media agent is associated with the first storage device and with the secondary copy of data; a client computing device comprising a data agent and a registry key; wherein the registry key is received from the second storage manager, and wherein the registry key associates the data agent with the first storage manager for restore operations originating in the first storage management system; wherein the data agent is configured in both: (a) a full-function client configuration in the second storage management system for participating in one or more storage operations managed by the second storage manager relative to data generated by the client computing device, and (b) a restore-only client configuration in the first storage management system, based at least in part on the registry key that associates the data agent with the first storage manager, wherein in the restore-only client configuration the data agent is configured to participate only in restore operations managed by the first storage manager relative to secondary copies of data stored in the first storage management system, including a restore operation in which the media agent and the data agent restore the secondary copy of data from the first storage device component of the first storage management system to at least one of the client computing device and a second data storage device in communication with the client computing device, wherein the restored secondary copy of data is accessible to the client computing device as primary data.