Logged-in user post to default username?

I was wondering if anyone has tried this or there is something in the codex I should start with.

I wanted to add a function to a form I created where a logged-in user can choose between publishing under their username or being able to choose to publish under a default name.

They would be only be able to choose that name, and won’t have any extra permissions. The “default” name is essentially an editorial name that represents all of our work.

Would there be a way to do this with the publish_post statement some user functions ( like set_current_user?). I am looking at front-end forms to see how a post is published, but am trying to find a way to allow someone to choose a default username which would be available to everyone. Thanks!