Yes, the author of a post can be changed after it has been created.
From the Compose page for the post, open the Authors menu above the Post Status, select an author, and click to Publish or Save the post.
The author of a Page can not be changed.
Updated 21 December 2015
Not quite what you are looking for? Check out these other articles:
- For information on importing a blog with multiple authors, check out the article on importing.
- Information on author permissions can be found in the Authors FAQ article.
- To create a custom, responsive design, you can use the Design Lab and choose for dozens of fonts for posts and pages.