excel file attachment

Hi

I need to be able to let people upload .xls files through the contact formula..

I’ve found that this is possible through adding xls to the standard file list

/* File type validation */

	// Default file-type restriction
	if ( '' == $file_type_pattern )
		$file_type_pattern = 'jpg|jpeg|png|gif|pdf|doc|docx|ppt|pptx|odt|avi|ogg|m4a|mov|mp3|mp4|mpg|wav|wmv|xls';

	$file_type_pattern = trim( $file_type_pattern, '|' );
	$file_type_pattern = '(' . $file_type_pattern . ')';
	$file_type_pattern = '/\.' . $file_type_pattern . '$/i';

contact-form-7/modules/file.php

So it isn’t impossible, but, is there a way to make this change permanent (I guess updating the plugin will erase my changes).

Thanks in advance,
Mark

https://www.ads-software.com/extend/plugins/contact-form-7/