Script doctors are a part of the development game. Writers are called in all the time to tweak or polish or shape or tinker with whatever the screenplay looks like, in order to tighten things up – dialogue, plot issues, character arcs, etc. – and get the movie into better shape than it was before they started working.
Big projects get this sort of attention all the time, with uncredited scribes you weren’t aware of on the film doing work under the cover of night. In most cases, the work goes unnoticed and/or unrecognized. This isn’t one of those times.
According to Birth.Movies.Death, Christopher McQuarrie was brought into the STAR WARS Galaxy to shine up ROGUE ONE: A STAR WARS STORY real nice, working out some of the story issues that were plaguing the standalone early on in production. According to the site's sources, "It's unlikely that McQuarrie will get a credit on the movie, although one source used the word 'saved' when talking about McQuarrie's contribution to the film."
It’s no surprise that it was McQuarrie’s number called, given his history with ensemble heist-style flicks (THE USUAL SUSPECTS and MISSION: IMPOSSIBLE – ROGUE NATION). Now the question is – Did he make ROGUE ONE any better? We’ll never really know. But, if, in December, you walk away from this story about the stealing of the Death Star plans by the Rebellion and you find yourself entertained, then McQuarrie did his job, however big or small it was.
ROGUE ONE: A STAR WARS STORY hits theaters on December 16, 2016.