I'm working on a code to farm whymsishire, and after every run it alsways puts the staff or herding back in my stash. How can I avoid this?
You could change the stash settings (in Settings > Loot > Right middle) to "Default - stash all legendaries" then it'll only stash legendaries.
The staff of herding is a legendary. I need a rule for this specific item.
You mean you don't want to stash all legendaries? and only stash specific legendaries?
You can choose "High" in stash settings, and modify Rules/High/Legendaries.txt, which has files rules to specify what items to stash.