Hi,
yes, but if you banned a category in an administration or delete it, I can not use my own field, and in the addition of the subject I will show up will show "Select Category" if I do not select the category I will not show my own added field
Addition: I've created one main category where I'm showing ads, but I do not want to see "Select Category" if it was set as the main one, so I only use visibility: hidenn in css