user/author is able to add new content to already existing article content

Hi,

I need a help ,

is that a user/author is able to add new content to already existing article content. The user should not be able to alter the original title, tags, location, or story that the original author included with the post Instead, the new author is able to embellish the original post with new other content with out changing previous user post.

If there any idea about this pls help .

Thank!