Sep 28, 2016 - 12:06 AM
As discussed on this article https://moz.com/blog/301-redirection-..., If a URL is properly redirected it has no affect on SEO. In fact if your old pages are not HTTPS, when we move your old pages from HTTP to HTTPS Google themselves are saying there is no loss of rank.
To make sure that you don't lose ranking you must:
1) Match TITLE / META TAGS from your old pages to the new pages
2) Make sure you redirect all URLs. You should check Google Analytics for your main organic traffic sources, and make sure all the old URLs are properly redirected to the new ones
3) Make sure the webpage content stays the same, it has to be above 70% similarity between the old and new page not to trigger a reindex.
If you are moving your content to an old domain and you want to make sure that you dont conflict the new domain with the old domain content, make sure you make the new domain more than 30% difference. The easiest way is to change the title, meta tags, descriptions. If you dont have time to change description you can put an RSS feed on every page with your recent blog posts (this feature is available in Shopping Cart Elite) and that will instantly make the webpage unique.