A render is when artists generate images through computer software, like sequences of lines or cubes. THIS "rendering" that you're referring to is a slang term that people who do these "renders" applied to these types of images, and aren't the sort of renderings deviantART means by the "3D and renders" category for submissions.
I know you may not understand this, but you are taking these images, editing them slightly, and posting them on your deviantART account, which is designed to be a webpage for artists who produce their own works from scratch. That, therefore, means you are violating deviantART's rules for submitting content, and are committing art theft.
Art theft is the number one way of being banned from this site. This is a fair warning, because you will likely be banned from deviantART permanently if you keep submitting these sorts of deviations.
deviantART is a site for people who create art by their own hands, or use their imagination to produce them. This sort of thing, while useful, isn't what deviantART is for. These "renders" are more for sites like TinyPic or Photobucket.
I'm sorry if I was harsh, but that's the way this site is. Potentially, if the original artist finds that you've "rendered" their works without permission, something as extreme as being SUED could potentially occur.