Hello!
That's certainly not a problem to do, though I need you top clarify on some things.
Like: You want the "archive" (category, tag) pages to display the posts like this, but not on the single post? Also should this still display the comments (replies) inline or should it list the posts only? And this is a "twitter" type of posting with this theme, so what do you actually refer to as a "headline" (there's no titles of the posts or anything, except teh ones made in teh admin and not front end)?
I can work on this right away, once we've cleared the listed above.
Regards,
Dobri