In screenwriting classes they say not to introduce a character by one name only to switch it later on. For example, introducing a character as BARTENDER only to change it to BOB two pages later for no reason. However this feels like a different situation than my problem.
In my script there is a character that, for the sake of an important reveal later on, lies about his identity to the protagonist. In the script right now, the character introduction has his real name, while in the dialog he is referred to by his fake name. This ruins the important reveal later for someone reading the script.
The best example from a movie I can think of is the movie Charade. In Charade, Cary Grant’s character goes through at least three or four names.
How is this handled format-wise?
— J. Jovel
In general, treat your reader like an audience member. As much as possible, you want to give readers the same information on the page that they would get on the screen. So if the character is introducing himself as “Mr. Truefake,” that’s what you should call him in the script.
In the third act, when it’s revealed that his real name is actually Ichabod Donnweather, it’s up to you whether you want to change his name in the scene description. If he’s only going to be sticking around for a page or two, you might consider using both names, like Truefake/Donnweather.
Another option is a quick explanatory note: “For clarity, we’ll continue to refer to him as Truefake.”
Either way, I’d advise you to keep using the original name in some form. Readers often lose track of characters, and changing up the names will generally make the situation worse.