Change WordPress regisration url with a url to a page of your choosing. Useful when you have a custom registration form

custom-wp-registration-url.php

<?php
/* 
* Custom registration url using WordPress register url filter 
* See https://wordpress.stackexchange.com/questions/127636/change-register-url-on-wp-login-page 
*/ 
add_filter( 'register_url', 'custom_register_url' );
function custom_register_url( $register_url )
{
    $register_url = get_permalink( $register_page_id = [REPLACE WITH YOUR PAGE ID HERE] );
    return $register_url;
}
/* end */