Easy Digital Downloads: Make software updates for free downloads possible without checking the license key

functions.php

<?php
/**
* Accept any license key for free downloads. 
* This assumes that license creation is enabled for the free download
*/
add_filter( 'edd_sl_id_license_match', function ( $license_match, $download_id ) {

	$download = edd_get_download( $download_id );

	if ( method_exists( $download, 'is_free' ) ) {
		if ( $download->is_free() ) {
			$license_match = true;
		}
	}

	return $license_match;

}, 20, 2 );