Can I swap drives to keep one off-site?

I also wish to swap my two WD drives as the prior poster described.  I have the same concerns and would like to clarify your response.

When I swap the drives, will the new drive automatically sync all the changed files on the computer?  If not, is there a way to force the drive to recognize all the changed files?

Do I need to delete the backup folder from the WD drive, to force it to start over and copy everything again?