Multiple Permalinks for custom post type post

Yes this is possible using add_rewrite_rule(), something along the lines of

add_rewrite_rule(
    'test-subject/(\d+)/?',
    'index.php?post_type=CPT_slug&post_id=$matches[1]'
);
add_rewrite_rule(
    'ts/(\d+)/?',
    'index.php?post_type=CPT_slug&post_id=$matches[1]'
);

It might be a bit trickier though, since test-subject/test-title and test-subject/post_id are quite similar. Adding the post_id-rule with the 3rd argument as 'top' might help.