Change Register/Lost Password “action links” URLs, titles & Modify Error pages. Theme My Login plugin driven Wordpress network multisite

Question

I have set up a huge a network multisite for my client which receives 1000\'s of new users per month and is already 5 clone network sites deep and counting It has a static Home

Answer 1

Here is the final working code I added just above /* Include popcorn.js --------------------- */ of functions.php after much testing and changing:

/* Filter to redirect register and lost password pages-------------WPN-09-03-2016--*/

function tml_action_url( $url, $action, $instance ) {
    if ( 'register' == $action )
        $url = 'https://EXTERNAL-REGISTRATION-PAGE/';
    elseif ( 'lostpassword' == $action )
        $url = 'https://EXTERNAL-PASSWORD-RESET-PAGE';
    return $url;
}
add_filter( 'tml_action_url', 'tml_action_url', 10, 3 );

/* Filter to change titles of links to above--------------------WPN-09-03-2016--*/

function tml_title( $title, $action ) {
    if ( is_user_logged_in() ) {
        $user = wp_get_current_user;
        if ( 'profile' == $action )
            $title = 'Your Profile';
        else
            $title = sprintf( 'Welcome, %s', $user->display_name );
    } else {
        switch ( $action ) {
            case 'register' :
                $title = 'Not a member? Register';
                break;
            case 'lostpassword':
                $title = 'Forgot your password? Reset it';
                break;
            case 'retrievepassword':
            case 'resetpass':
            case 'rp':
            case 'login':
            default:
                $title = 'Sign In';
        }
    }
    return $title;
}
add_filter( 'tml_title', 'tml_title', 11, 2 );

/* Filter to change link in user error message------------------WPN-10-03-2016--*/

function login_error_message($error){
    //check if that's the error you are looking for
    $pos = strpos($error, 'incorrect');
    if (is_int($pos)) {
        //its the right error so you can overwrite it
        $error = "<strong>ERROR</strong>: Invalid username/password. <a href= https://EXTERNAL-PASSWORD-RESET-PAGE/>Lost Password?</a>";
    }
    else $error = "<strong>ERROR</strong>: Invalid username/password. <a href= https://EXTERNAL-PASSWORD-RESET-PAGE/>Lost Password?</a>";
    return $error;
}
add_filter('login_errors','login_error_message');

Kudos to Igor Yavych who bailed me out while I was making a rookie mistake very early hours of the morning after no sleep last night while experimenting with code to finally get the working result! ( See here: Wordpress PHP issue in functions.php regarding if and else if statement )