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Hi, If you change content, design and URLs in the same time you won't be able to assess the reason behind an improvement in rankings or a negative effect in rankings. Let's say you change all 3 in the same time and you get a slight increasing rankings - you will be happy but the setup behind this is that the content change had a huge positive impact and the design and url changes had a negative effect - you only see the final end result  - this is just an example. The bottom line is that you can get the best out of it if you do it step by step as you can adjust, roll back, edit in order to get the best out of it. The last change I would do is the URL change and always have a fix and clear procedure in place for this as it is important (if you have some visibility now and the risk of losing something is big). Cheers.