The goal of the reshoots, according to THR, is to “lighten the mood, bring some levity into the story and restore a sense of fun to the adventure.”
It might sound melodramatic but the more I think about this sentence the more heartbreaking it gets. It shows that those making the decisions have an apparent fundamental lack of understanding about what story they're attempting to tell and are striving to screw it up.
Down to brass tacks the trailer presented the movie as the story of how the Rebels got the Death Star Plans. Basically what we're talking is a special forces espionage heist film set in the middle of a war. What about that premise says "light, humorous, frivolous, fun, adventure"?
While at it do they plan to retcon, "Many Bothans died to bring us this information," to "A couple Bothans suffered muscle strains..."