Update Pay by Check wording to something else.

my_gettext_pay_by_check.php

<?php
/**
 * This recipe changes the "Pay by Check" language
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * @link http://codex.wordpress.org/Plugin_API/Filter_Reference/gettext
 * @link https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
*/
function my_gettext_pay_by_check($translated_text, $text, $domain)
{
	if($domain == "pmpro-pay-by-check" && $text == "Pay by Check")
		$translated_text = "Pay by invoice";		//change the text here
	
	return $translated_text;
}
add_filter('gettext', 'my_gettext_pay_by_check', 10, 3);