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it is appropriate when you update to content, add new elements, add new text or images BUT If you are talking about changing the URL of ranked BLOGs then you should think 100 times before adding even a one character in your url. I did it with Hiking watch site and observed not suitable results that was I was receiving before. So Plz do it carefully/
I think you should focus on sites or forums which are related to your niche/topic. Then you should outreach for contextual backlinks from authority sites that link to related blogs and have links from related blogs. Their outbound OBL should be low that will help you to increase your DA and traffic in a white hat way.