Hello Edorta,

yes, you can.

To have a specific url to a category page, just add the category name at the end of /portfolio_category.

For example

http://clapat.ro/berger-wordpress/portfolio_category/branding/

to exclude a category from the portfolio page is a bit more complicated

If you open portfolio-page.php you need to modify two queries:

first the one that selects all categories:

 $portfolio_category = get_terms('portfolio_category', array( 'hide_empty' => 0 ));

https://developer.wordpress.org/reference/functions/get_terms/#parameters

see 'exclude' parameter

Second is to modify the arguments of the query that selects all portfolio posts:

$args = array(
                    'post_type' => THEME_ID . '_portfolio',
'paged' => $paged,
'posts_per_page' => 1000,
                         );

http://wordpress.stackexchange.com/questions/142484/exclude-custom-taxonomies

https://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters