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So I’m this vein the 4 is this house number, f is position in the house, and cast is obviously tagout/rotation/bump/spot swap?
Correct, the casting e-mails for houses will say, for example, 'H4' for House 4, and then which cast, A or B. Streets are slightly different as they will say 'S4' for Street 4 and the cast you're on but I believe they have more than 2 casts for streets, but I'm not 100% sure on that.
How would one know the letter that correlates with those characteristics? Like how does one know what signifies “shaved head”, for instance?
Special requests such as shaving your head is asked during auditions and then reflected in the casting e-mail you're sent so you know if you need to alter your appearance or not.