When a mystery shopper accepts a shop, he agrees to do the shop according to the guidelines the customer provides. If he can't, he should not take the shop. If the shopper forgets and uses his Crown Club Card, the shop is not accepted and the shopper is not paid. If the shopper activates the points after the fact, the consequences could probably include non-payment and might be labeled fraud by the MSC. That would likely mean deactivation.
When I go to the Regal theaters on my own dime, I do what I want. When I am working, I follow the client's rules.