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I don't think there is a problem in removing the 301s.  You are not doing anything underhand.  The 301 is in place because for whatever reason you have decided it is better for your visitor to reach the redirected page.  There could be many valid reasons why the original pages are now valid, you aren't always to know a redirect is definitely temporary. Just in the same way you may need to amend a 301 to a new URL. However, I would introduce the URLs back in small batches and monitor rankings and traffic.