So far as I know there never was a non-electric boot release (ie a manual lever). The key/lock is simply pulling a wire/rod (like a bit of straight coat hanger). If that was accessible externally, that would open the boot, but bypass the key -- ie the boot would not be locked. To add the electric version may be more effort than just replacing the lock with the electrically-opened version. Clearly a new boot handle with the switch, but maybe a bit more wiring too.