Hi Guys,

I will explain the process below, how that can be done.

1) I would recommend to add the following snippet in the functions.php of the child theme. This will create the tags as taxonomy and assign it to the portfolio post type.

/**
 * Portfolio Tags
 */
function neuron_portfolio_tags() {
    $labels = array(
        'name'                       => __('Portfolio Tags', 'neuron-core'),
        'singular_name'              => __('Portfolio Tag', 'neuron-core'),
        'menu_name'                  => __('Portfolio Tags', 'neuron-core'),
        'edit_item'                  => __('Edit Portfolio Tag', 'neuron-core'),
        'update_item'                => __('Update Portfolio Tag', 'neuron-core'),
        'add_new_item'               => __('Add New Portfolio Tag', 'neuron-core'),
        'new_item_name'              => __('New Portfolio Tag Name', 'neuron-core'),
        'parent_item'                => __('Parent Portfolio Tag', 'neuron-core'),
        'parent_item_colon'          => __('Parent Portfolio Tag:', 'neuron-core'),
        'all_items'                  => __('All Portfolio Tags', 'neuron-core'),
        'search_items'               => __('Search Portfolio Tags', 'neuron-core'),
        'popular_items'              => __('Popular Portfolio Tags', 'neuron-core'),
        'separate_items_with_commas' => __('Separate portfolio tags with commas', 'neuron-core'),
        'add_or_remove_items'        => __('Add or remove portfolio tags', 'neuron-core'),
        'choose_from_most_used'      => __('Choose from the most used portfolio tags', 'neuron-core'),
        'not_found'                  => __('No portfolio tags found.', 'neuron-core'),
        'items_list_navigation'      => __('Portfolio tags list navigation', 'neuron-core'),
        'items_list'                 => __('Portfolio tags list', 'neuron-core'),
    );
    $args = array(
        'labels'            => $labels,
        'public'            => true,
        'show_in_nav_menus' => true,
        'show_ui'           => true,
        'show_tagcloud'     => true,
        'hierarchical'      => true,
        'rewrite'           => array('slug' => 'portfolio_tags'),
        'show_admin_column' => true,
        'query_var'         => true,
    );
    register_taxonomy('portfolio_tags', 'portfolio', $args);
}
/**
 * Add Tags to Portfolio
 */
function neuron_custom_portfolio_tags() {
 neuron_portfolio_tags();
}
add_action('init', 'neuron_custom_portfolio_tags');

2) The next changes needs to be done directly on the plugin(Neuron Core).

Open filters.php which is located in neuron-core > widgets > posts > templates > filters.php and add the following snippet. http://prntscr.com/neho8f

/**
 * Override
 */
if ($settings['posts_type'] == 'portfolio') {
    $neuron_posts_taxonomy = 'portfolio_tags';
    $post_terms = get_terms('portfolio_tags');
    if ($post_terms && !is_wp_error($post_terms)) {
        foreach ($post_terms as $term) {
            $post_categories[$term->slug] = $term->name;    
        }
    }
    $neuron_posts_normal_query = $post_categories;
}

In the file layout-isotope.php  which is located at neuron-core > widgets > posts > layout > layout-isotope.php in the line 137 replace $neuron_posts_taxonomy with 'portfolio_tags'

- http://prntscr.com/nehojm 

I have tested this on my localhost, everything worked alright, do not forget to flush the permalinks(click save changes on the Settings > Permalinks).

Feel free to ask for anything you need :)

Kind Regards,
NeuronThemes