Those texts are texts for Module A. I'm not sure about what you're teacher is saying; Frankenstein is a book, and Blade Runner is a movie, and they are texts of their own offered for study in Module A, so it's quite obvious you're allowed to do so. That being said, I don't recommend you try and switch texts last minute. If you are basing this predicament off the fact that you have a better F/BR essay than G/B, then I suggest you reconsider. You simply will not have studied either texts as well as Gastby and Browning (as you didn't cover it in class) so if the question is a bit difficult, you're left with this awkward essay that's good in its own respect, but possibly un-adaptable and largely irrelevant to the question. But you do mention you studied it in another institution, so I'm guessing by that you mean a tutoring college of some sort? If that is the case, then just make sure you know the F/BR texts well enough to be able to easily add quotes/techniques/ideas if necessary. I wouldn't recommend it, but if you genuinely feel like you are more comfortable and knowledgeable of F/BR than G/B then I guess you should try it.