The cast's contracts guarantee them a set number of appearances over a set time, and outside those times they are allowed to take on other work, subject to Granada's approval.
Cast members are not allowed to radically alter their appearance, unless for example the storyline dictates that the character has been on holiday, in which case a sun tan is OK, but changing of hair colour and style, addition of loss of facial hair, weight gain or loss, and so on, are all forbidden.
Older AB'ers may remember Lynn Perrie who played Ivy Tildsley hastening her exit after notable lip enhancement surgery during time away from the Street.