Can a post contain modified version to be published at later date?

I am looking for a way to accomplish the following with WordPress:

– Create a post with CONTENT A, to be published today.
– Create a second version of the same post, this time CONTENT A MODIFIED, to be published tomorrow, by REPLACING the original post. Meaning, it simply replaces the original post, without affecting the original release date, but will now show the Modified Version.

Is this possible? straight out of the box, or perhaps with a plugin?

My usage of this idea is for the following workflow:

I have a website where I post news every few days. Each post contain a large image, like a magazine cover for instance. I would like to be able to have that image be replaced with a smaller size when a new post is published. This way, only the top post of the website shows a large size cover image, while the posts below previously published will show smaller versions of the originally published covers.

Makes sense?

Any ideas, suggestions?