You can override the author link via the author_link
filter:
function wpd_author_link( $link, $author_id, $author_nicename ){
return 'http://my.blog.tld/';
}
add_filter( 'author_link', 'wpd_author_link', 20, 3 );
$author_id
and $author_nicename
are available to the filter so you can fetch whatever data you need to generate the correct link.