If you have a number of posts that have been wrongly assigned to a category, it’s easy enough to use the bulk add feature in the WordPress admin to add a NEW category but can be tricky to remove the erroneous category you no longer want.

WordPress lets you programmatically set categories from an array with “wp_set_post_categories” but to remove you first need to remove the offending category. To do this, I wrote a little function that loops through the categories and skips over the one you don’t want (id # 307 in this example but this is where you’d add the id of the category you want to remove if reusing) to rebuild a “clean” array:

function surgo_remove_inbox_cat_id($thepostid, $taxonomies, $args) {
	
	$tags = wp_get_object_terms( $thepostid, $taxonomies, $args );
	
	if ($tags) {		
	$tagswithoutinboxarray = array();
		
	  foreach($tags as $tag) {
	  
	  	  		if ($tag->term_id != 307) {
	  
	  					$tagswithoutinboxarray[] = $tag->term_id; 
	 
	  			}
	  
	  }
	   
	  return $tagswithoutinboxarray;
	
	}
}

Then just pass this clean array to the wp_set_post_categories function with the post id and you’re good to go.