From what I have seen in your screenie there you are trying to modify a core item. I found at least you generally have to duplicate the item to be able to modify the data therein. Modifying race data is slightly different then regular units and other items since you also have to set it in the properties of the map as well.
But if you duplicate it then you should be able to modify those values.
And as @DirectorOfTheUED: said, the text view is a lot more efficient and more intuitive. Set this in View/Set Table View