I'm writing a screenplay in which a character is thought to be called one name for the first act, after which it's revealed that his name is actually something else. For the dialogue tags and descriptions, is it appropriate to change the name used at this point, thus potentially confusing the reader, or should I keep the same name throughout, thus cluing the reader in to the twist before the other characters (and audience) know?
I actually had a slightly more complicated version of this problem in one of my specs, so here's how I dealt with it:
Let's say the name we know him by in the first act is "Greg." Just call him "Greg" in the start. I got even trickier with my naming and introduced the character as "MAN" until someone called him by the name "Rick." Then, in the next dialogue header, I referred to him as "MAN/RICK," and "RICK" in every subsequent instance until it was revealed that his name wasn't Rick, it was "Steve." At that point, I had the next header call him "RICK/STEVE" and then wrote "Note: from this point on, the character we have referred to as Rick will now be called Steve."
You could probably simplify that a little bit, or vary the method, but I found that to be effective. I wouldn't use his "real" name until it's identified as such to the characters, though.