When X job complete, update Y

I'd like to be able to automatically mark the Accounts records as Received once the final VAT quarter of the year has been marked as complete. If it were possible to bring in some sort of options or conditions, on the basis of if X task is marked as complete, then do Y - in this case: if VAT = complete, then Accounts = received. I'm sure this would be able to be used for a whole range of other things too if it's given enough funcitonality and options.