According to me you can make some changes in your content it will be beneficial for you and people will get to read something new and fresh. Although if someone is coping content from your blog it will not cause any kind of harm to your blog. Google has each and every update
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That’s bad. But if your content gets “crawled” first by Google, your site (the one that posted that content) will get the rank first than the duplicated one in other sites. I don’t know how Google treats duplicated content. Others say that Google will count similar content as one vote or it gets penalized (the copyist) unless it is clear that the article syndicated. As I’ve said I’m not sure and I could be wrong.
Since it’s posted without your permission, you can file a suit online. I think you should talk first to the copyist. See to it if he/she agrees to take down the copied content or not. If not, then you know what to do.
Duplicate content is harmful for the website. if your site content is dulicate, your site ranking will be decrease.