Altering Create New account tab link in user login page
Well, you could use hook_menu_alter() to change the call back function of that menu item:

function MY_MODULE_menu_alter(&amp;$items) {
  $items['user/register']['page callback'] = 'my_custom_function';
}


And then you could redirect to a new page in the callback:

function my_custom_function() {
  drupal_goto('customlink');
}