I think that’s the one James uses on Snape, but you are right- Harry doesn’t try it out until he uses it on Ron in HPB. I remember Lupin or Sirius saying that it was the “fashionable” charm to use when they were in school.
The other thing I thought was odd was that Umbridge blasts through the door of the room of requirement. How are they going to rectify that with Harry trying to get inside it in HBP? People who aren’t familiar with the books will probably just think, “Why doesn’t he just blast through like Umbridge did?”
Harry asked for a room to train and practice DADA. (Although what Neville asked for in the movie is unclear.)
Malfoy asked for a room where he wouldn’t be disturbed.
The other thing I thought was odd was that Umbridge blasts through the door of the room of requirement. ..........
If you know the purpose of the room, you can enter. Remember Cho’s friend told them the purpose of the room, so she was able to come in. Of course, like you pointed out though if the audience didn’t read the book, then they won’t know this info and will be confused.
Correct and Umbridge uses a spell that Hermione used in Prisoner of Azkaban to break Sirus free. “Bombarda!”