In a smart in-joke, Solo: A Star Wars Story actually acknowledged its own directorial problems. Partway through production, the latest Star Wars spin-off suffered a blow when directors Phil Lord and Chris Miller parted ways with Lucasfilm. The studio swiftly called in Ron Howard to sort out the problems, and Howard is believed to have reshot "nearly all" the film at "twice the budget."
Nobody actually knows what happened behind the scenes on Solo, but by all accounts Lucasfilm and the directors were clashing from early on. Lucasfilm is proud of Solo's script, while Lord and Miller are known for their improv style. According to the rumors, that was the source of the conflict, with the directors deviating from the script far more than the studio liked. If these accounts are true, then the differences between the studio and the directors ultimately became impossible to resolve.
Leave it to Solo to actually acknowledge this in a quickfire (potentially meta) quip that will make any aware viewers laugh out loud.
Bring on the Improv
There's one specific scene in the mines of Kessel where Beckett is issuing orders. He clearly already has a good read on the young Han Solo, as he turns to Han and barks out; "Stick to the plan. Do not improvise." It fits with the scene and makes perfect sense in terms of the dialogue, but (intentionally or not) it also means so much more. In light of the movie's director troubles, it succinctly sums up the differences between the studio and the directors in just two sentences; Lucasfilm wanted Lord and Miller to stick to the plan, while the directors wanted to improvise. It's a brilliant nod, and it's sure to amuse viewers familiar with the drama. Meanwhile, the line takes on an even greater meaning when you remember that Harrison Ford - a.k.a. the older Han Solo - is a master of improv. He ad-libbed the famous "I know" response in The Empire Strikes Back, in perhaps the most famous example.
But, appropriately enough, there's even more to it than that. Lucasfilm released an official tie-in novel for Solo, Rae Carson's Most Wanted, and that fleshes out the relationship between Han and Qi'ra. It reveals that Qi'ra is a master planner who spends hours working out the best course of action before she finally acts. Han, in contrasts, is known for his instinctive, improvisational style. The two realize there's a place for both approaches, with Qi'ra dubbing Han "Improv Guy." Qi'ra, in turn, gains the nickname "Plan Girl." That backstory adds another layer of humor to the scene because even as Beckett issued that order, Qi'ra would be watching knowingly, well aware that improvisation is Han's specialty.
Just as in the novel, Solo ultimately sees the sneak-thieves find a place of balance. The plan is working (just about), but even Beckett has to acknowledge that there's a time to improvise. When that time comes, Han Solo is the man you really want on your side. It's a nice way to resolve the joke, suggesting that a balance can be struck between the two. Hopefully Lucasfilm found that balance as effectively as Beckett and Han.