to force an ID you have to insert a string so:
up_down_post_votes( get_the_ID(‘500’) );
but why force a not exist number??
also the category as an unique id, it’s registered into the _term_taxonomy table and it’s the number you see in the admin url, for example “..taxonomy=category&tag_ID=2..”
working “a little” you could take the category id into the meta of the post, to allow to vote the category and then eventually into the category page.
