I saw the manual rules announcement - Introducing manual rule triggers! - News / Product Updates - Asana Forum - and got super excited. I then realized that the function to run it on an entire project was missing. This is actually what I was hoping for, so we can create rules for some data maintenance activities, run them once and move on.
I feel like the only weak area of Asana is that everything seems to run client side. It would be great if this function could work server side so it could trundle through hundreds or thousands of tasks and clean them up without sync issues.