How I can change the condition or compare operator for WP_Query in pre_get_posts
You can achieve the OR relation using the tax_query argument like so: $query->set( ‘tax_query’, array( ‘relation’ => ‘OR’, array( ‘taxonomy’ => ‘category’, ‘terms’ => array( 2, 3 ), ), array( ‘taxonomy’ => ‘post_tag’, ‘terms’ => array( 10, 13 ), ), ) );