I’m not sure what you want to ask. Or what you want to do.
To the “Download” post type (this is a custom post type), we can add “custom-fields” support.
A php function should be added to this operation.
Then there would be a custom fields setting, like “Post” defuault post type. You can turn this on when editing on the “Screen Options” tab.
Would you need that?
I’ll show you a mockup:

So, some way to add these in the admin front-end which I then can access in my own functions, if that makes any sense.
So meta fields for taxonomy.
I think the easiest way to do this is to use the ACF plugin.
Thanks, I’ll check it out. :]
That worked better than expected. Thanks for the tip!