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I would create a new webmaster property instead of trying to change the address of two sites. Are you setting the new site up as HTTPS? What are you doing with the old domains? I would make sure you keep the registration active on them so that no one else can buy them. Aside from refreshing content and HTML data, creating a new Webmaster property, monitoring performance and verifying that the dynamic 301s are working I can't think of anything else really.

Hi Matt, When you say submitting urls to google I assume you mean via a sitemap in GWT? If so there is no reason for the url changes to cause any issues/penalties - you already have a sitemap with the old urls right? So the new one would have a similar number of urls simply with different paths to the same content... no problems there. The biggest threat to organic traffic is not having complete and proper 301 redirects in place for all (or most) pages which can potentially cause quite a bit of damage so make sure you have covered all the bases for the 301s!