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Hi Sandra I would: take away the old 301s establish a sitewide 301 redirect from your current to your "old" domain definitely use Webmaster Tools to indicate the domain change to Google. This really speeds things up. However, don't expect your rankings to go back to normal again - it normally takes a few months to earn the old domain trust again. Also, make sure that the domain you're migrating back to is clean and safe (i.e. never used for spam and a clean link profile). Hope this helps!

How you phrased your question, I thought you were considering only moving pages that didn't have any backlinks, not the entire subfolder. You want to keep your URLs consistent, and it's pretty easy to build 301 redirects around an entire subfolder.