In the second year, Barbara Bain had it written into Catherine Schell's contract that she never appear as "Catherine Schell" - only as Maya or a totally different actress if she were to play a human female. Nobody could be prettier than Barbara Bain (no comment).
I can understand protecting the size of your role (although it greatly reduces the series' storytelling latitude), but protecting your status as the best-looking is a little bit sad. And forcing clauses into someone else's contract really smells.
I actually joined yesterday btw, but they put you on hold for a day and make you take an oath attesting that you aren't a robot or a salesman.