is it possible to create a post, logged in as admin, and changed the name from the author? after publishing? or is it possible without login to other users , to create a post, and change the name from the author? You know what i mean?
Are you trying to do this programmatically? It's certainly possible to be logged in and change the author of any post. It's even part of the "Quick Edit" menu, or you can go to the post, select "Edit". The post author select menu is at the bottom of every post (or page) in the Classic Editor or in the right column in the Gutenberg editor.