If you are talking about the ability to load CSS files through the CssFiles
property of RadEditor then you can implement your own WebPart that will load different file(s) through the CssFiles property according to the logged user.
if (UserRole == "Admin")
else RadEditor1.CssFiles.Add(new EditorCssFile("~/Css/Common.css"));
If your scenario is other please explain it in more details.
the Telerik team