Whenever overridden, you will have to either:
Save the old function and call it after your current one
or
You would have to have return behaviorLib.pickRune(botBrain, behaviorLib.runeToPick) at the end
And either way, you'd have to have behaviorLib.PickRuneBehavior["Execute"] = behaviorLib.PickRuneExecute at the end..
My way, you just override behaviorLib.CustomMoveToRuneExecute, it'll give you the location of the rune, and all you have to do is use skills and return true or false.