For reusable top level containers, we need to export the components as .xdc file. These .xdc can be imported so as to reuse the components: http://docs.sencha.com/architect/2/#.../collaboration
If there are changes done later in the reusable top level containers, as of SA 3.x preview version, we first need to delete the previous component and then re-import the modified .xdc file again.
As it has been said that SA 3 release version will maintain versioning for user extension modifications. Do this version controlling mechanism be available for .xdc files too ?