I would like to set/unset a property when entering a certain `TODO` state. 

Example: Set the property `:COOKIE_DATA: todo recursive` automatically when the state is set to `PROJ`. So all the `TODO`s in project headings would be counted recursively.

How could this be done?

I do *not* want to set `org-hierarchical-todo-statistics` to activate recursive counting for every `TODO` globally.