This gets placed in your theme’s functions.php… ‘Signup’ is the text for the register link in this example. ‘Logout’ is the message displayed when the user is logged in. That could easily be a link to their profile or the admin area as well.

add_action( ‘register’ , ‘register_replacement’ );
function register_replacement( $link ){
if ( ! is_user_logged_in() ) {
if ( get_option(‘users_can_register’) )
$link = $before . ‘<a href=”‘ . site_url(‘wp-login.php?action=register’, ‘login’) . ‘”>’ . __(‘Signup’) . ‘</a>’ . $after;
else
$link = ”;
} else {
$link = $before . ‘<a href=”‘ . wp_logout_url() . ‘”>’ . __(‘Logout’) . ‘</a>’ . $after;
}
return $link;
}