Actors can provide notes about their characters but the writing and pre-production is typically done far in advance before they’ve received the scripts. Especially with the sets, locations and VFX Stranger Things are dealing with. Dialogue and character beats can be done more in the moment, but Stranger Things is a machine with a ton of moving parts. Changing things on the whim for actors would mean changing the work of a ton of crew and budgeting.

Show Runners can discuss with the actors before the writing happens and get feedback, but in the end it’s up to them. They have the full scope of the story whereas an actor only typically has their portion.