It is not possible to either initially set and later change line endings.

Since multiple types of line endings are supported depending on the initial file's extension, it is critical to be able to change them later if you either rename a file or change its syntax definition dynamically. For example any CR terminated file won't render as Markdown, even if you rename it. I also recommend an option a file creation time to set the line endings as well, but it's not as important as being able to change them.