You seem to want to give the categories a 'index' number according to its 'depth'. And that this 'index' is not in the title of the Category or subcat.Is that correct?
The Title does, by default, set the alias and the name of the directory that holds the data.
As a demo I setup some categories and subcats, then used the Direcroy name as the extra identifier see pic. The directory where the Downloadabke files will be stored was made the same as the last part of the cal/subcat title.To be able to freely set the directory name use Options -Files And Folders tab - 'Create the Directory Name automatically' to No.
But I am not sure if that is what you want.
I may be able to help more if you could explain why you need the extra 'field' or identifier.