Yes you can. Here is how you should do it:

First create a new login profile for the server with the new address/file system location:

1. Go to the login profiles list in the preferences.
2. Select the login profile with the old server details.
3. Change its "Description" to a new one (e.g. append the string 'new' to the end).
4. Update the server details so they reflect the new repository.
5. Click the "New" button.
6. Click OK to close the preferences.

Now change your sandbox:

1. Open the sandbox folder in MacCVSClient.
2. Select menu command "Special/Reroot Sandbox...".
3. Select the login profile with the new server details.
4. Click OK in the reroot sandbox dialog.
5. Click OK again in the confirmation dialog.

You can then remove from the preferences the login profile which refers to the old repository.