Change Permalink Structure without Affecting Old URLs?

It probably will ruin backlinks. Have you considered looking into adding 301 redirect code to your htaccess? This would solve the problem but you would need to take not that it is there in the case you decide to switch back or change to an different permalink structure again down the road.

Take a look at this article for assistance with writing the 301 redirects necessary: https://www.goinflow.com/setting-up-301-redirects-for-dynamic-urls/

Hope this helps!

I appreciate your comment, but a 301 redirect passes between 90-99% of link juice to the redirected page.

I was hoping to leave the old urls intact while changing the future urls to the new format.

Actually, 301 redirects pass 100% of the back links to the correct place.

I use them all the time and never have any problems.

I was going by the information posted here:
https://moz.com/learn/seo/redirection

What they are saying there is that it transfers 90-99% of the SEO rank from the old link. However, anyone use uses the old link will definitely still get the correct page.

So, you want to change from example.com/shop/category/product-name
to : example.com/product-name

This means that the SEO rank for example.com/shop/category/product-name could decrease since you are changing the url structure. There is no way around this though unless you want to lose the SEO rank all together.

Hopefully that makes helps to clarify the situation for you.

301 redirects are basically the only way I know of to be sure that the old link structure does not get completely lost and I have been developing websites for ten years.