disable-custom-text-settings.php

<?php
/**
 * Turn off custom text settings.
 */
function my_mrp_before_init() {
	add_filter( 'mrp_disable_custom_text', 'my_mrp_disable_custom_text', 10, 1 );
}
add_action( 'mrp_before_init', 'my_mrp_before_init', 11, 0 );

/**
 * Returns true
 * 
 * @param unknown $value
 * @return boolean
 */
function my_mrp_disable_custom_text( $value ) {
	return true;
}