I believe you can set the default term when you register the taxonomy. See the default_term param for register_taxonomy in the documentation. So this feels like it should be handled when setting up the taxonomy.
whether a category can be removed
For this, do you mean whether or not that taxonomy term selection is required?
You should be able to make a taxonomy semi-required by removing the “no term” option. You can achieve this via the following snippet:
add_filter( "radio_buttons_for_taxonomies_no_term_{$taxonomy}", "__return_FALSE" );
Though you might then run into the problem of not having a selection at all (unless you have the default set). I agree a UI for that would be nice. And some error/notice prompting when not selected would needed to really force a selection.
Thank you very much for your quick reply. Yes, that really helps to fill the missing desired functions. But it would still be helpful if this was already available in the plugin options, especially for those who are not so good in PHP.
But thanks anyway, and I would have given four and a half stars now, but so be it.
