Conditionally loading a custom template in WordPress. https://since1979.dev/snippet-006-conditionally-loading-a-custom-template/

wp-template-redirect.php

<?php
/**
 * template_include_callback.
 *
 * Maybe redirect to a different template file
 *
 * @see https://since1979.dev/snippet-006-conditionally-loading-a-custom-template/
 *
 * @uses is_page https://developer.wordpress.org/reference/functions/is_page/
 * @uses locate_template https://developer.wordpress.org/reference/functions/locate_template/
 *
 * @param String $template The path of the template to include.
 * @return String
 */
function template_include_callback(String $template)
{
    if (is_page(148))
        return locate_template('contact.php');

    return $template;
}

/**
 * Hook: template_include.
 *
 * @uses add_action() https://developer.wordpress.org/reference/functions/add_action/
 * @uses template_include https://developer.wordpress.org/reference/hooks/template_include/
 */
add_filter('template_include', 'template_include_callback', 100, 1);
?>