probably wouldn’t take off, but if you could step in to a movie and change the course of it with your knowledge of how it actually ends would be a bit of fun.
For example in Die Hard 3 I’d of told Bruce Willis to stay in the Cab with Samuel L Jackson as the reason Irons used for blowing up the train was that they both didn’t make the phone booth on time, Willis got out the car because he thought it’d be unlikely they’d make it, Jackson made it with ease. Surprisingly later in the film they reference that they had no chance of making it, if Willis had of just stayed in the Cab they would’ve.