Theme my login replacement variables filter. Used to add your own variables to the Custom Emails module of theme my login. Uses tml_replace_vars.

functions.php

function custom_email_replace($old_replacements, $user_id){

    // Generate the new url we need for this user
    $enrollment_form_url = 'special-url-'.$user_id;
    
    // An array of our replacement variables and their values
    $new_replacements = array(
        '%enrollmentform%'=> $enrollment_form_url,
    );
    // Merge our two arrays together
    $replacements = array_merge($old_replacements, $new_replacements);
    
    // Return the array of all the replacements
    return $replacements;
}
add_filter( 'tml_replace_vars', 'custom_email_replace', 99, 2 );