whats the difference between rewriting articles that are PLR and arent? isnt the content different anyway after it has been rewritten?
The vast majority of "rewritten" content isn't actually rewritten - a few words may have been changed here and there to make it pass a copyscape test, but that doesn't mean it's ORIGINAL content. You are better off creating articles that are unique rather than ripping off someone else's hard work and contributing to the plethora of regurgitated crap already on the web. Not to mention, plagiarism in any form is ILLEGAL.
Denise is right. It's illegal to rewrite content without having the rights to it (copyright, PLR license that allows it, etc.). There's no "safe" percentage legally that you can change someone else's work and not be in violation of their copyright, and you can't make derived works from theirs without permission like that. Just as an example where even 100% changing wouldn't likely protect you: while lists generally can't be copyright protected, "creative" lists can be. If you were to take someone's list that does fall within protection guidelines and reorder everything, even though you may have changed it 100% in the eyes of search engines and some readers, you would still be in violation of copyright laws.