Would this also work if you want to only be able to navigate a few of the categories? For instance, only allow it to go from categories 1,2,3 and not 4 or 5. Say, something like this:

add_filter(‘avia_post_nav_categories’, ‘avf_same_category_filter’);
function avf_same_category_filter($same_category)
{
$same_category = true;
return $category1, category2, category3;
}

??