Steven Zahm@ James
The only thing I can think of is you’re editing/uploading the the wrong file somehow.
What is the exact full path of the file and folder you’re editing? Try using the Plugin Editor to make the change instead. Using the plugin editor will ensure the correct file is being edited.
Another thought … do you have any type of page caching being utilized via the server or WordPress plugin?
Not sure I understand your “drill down” question, but I think you mean chained selects. If that is the case, sorry, no. The best that can be done is enabling the beta feature, multiple select. This changes the drop down into a drop down that permits multiple categories to be selected at once. For an entry to return as a result it will have to be assigned every category that the use chooses. I hope that makes sense!
Seems you figured out how to remove the individual option in Form.