Truth is, it'd actually be a LOT harder, and probably involve a lot more work. I can imagine now, getting a call from Producer Dude:
"Good news and bad news guys. Dakota Fanning's people got ahold of the script and she loves it. They want to know if we can rewrite the 'wife' role to be a daughter."
And, of course, we'd all scramble to make it happen. I mean... it's Dakota Fanning. She's box office gold. Plus everyone knows she's a ruthless tyrant who'd have our heads on a pike if we did anything short of take a Bic to the script in order to make it work for her.
But that's not the world we live in. Dakota Fanning will never know this movie exists, much less read the script. Best case scenario, she's on a press junket in Taiwan two years from now, plugging some Spielberg thing she's starring in for $10 million and happens to flip by our flick playing on the Taiwanese equivalent to Cinemax at 2am while she desperately hunts for Nickelodeon.
Indeed, in our world, calls from Producer Dude go more like this:
"Dude. I just got off the phone with one of the investors. His cousin Bjorn really wants to break into acting, so they'd like to find a way to work him into the movie..."
"Ok. I'm sure we can come up with something."
"... as the lead."
"Ah. I see. Well... that's really a business and creative decision. We're just the writers. I'm sure you'll do whatever's best for the..."
"He's Swedish."
"Ok. That may be a bit odd, as our lead is a former US Army Special Forces guy. And black. But we'll find a way to work through it."
"And he doesn't speak English. I have faith you'll figure it out. Talk to you soon."
At which point Dave and I would engage in a Writer's Deathmatch to determine who wins the prize for taking first pass at THAT revision.
See? As much as things are DIFFERENT in the "real budget" versus "b budget" worlds, they're similar, too. The scale of issues is just different. You do rewrites for business-driven reasons. You tweak for cast members that are dictated by unseen forces pulling purse-strings. Creative is key, but only insomuch as it supports a clear business objective.
Which is fine... there's a reason its called Show-BUSINESS. I can subvert my creative urges in order to further the film's success on the funding/sales/distribution front.
Just so long as we don't find ourselves working on "An American Hero II," starring Bjorn Skaarskaargaardaang as our next project.
Charlie
* The above conversation has never actually taken place. But its the kinda call I could imagine us getting.
** I'm just kidding about the Dakota-is-a-tyrant thing. I'm sure she's a delightful young lady. Please don't kill us, Dakota.