Does marginally changing a well established domains URLs and page content affect site ranking in search engines

I am rewriting a web application and will be porting procedural PHP code to a framework.

At the same time, the layout of the pages (but not the critical content) is not changing.

I'm thinking that I need to some how port the old URLs by using a 301 Redirect permanent.

Any advice on how to proceed? As this site is long established with a good reputatio开发者_如何学Pythonn, it's important we maintain rankings in Bing and Google.

Thanks.

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You should use 301 redirects instead, that will carry over the data the engines have for those pages and you should be fine