Changing name of the uploaded file.

[eluser]DADE[/eluser]
Well, I found solution.

system/libraries/Upload.php file, _prep_filename() function, line 994

Code:

protected function _prep_filename($filename)
    {
        if (strpos($filename, '.') === FALSE OR $this->allowed_types == '*')
        {
            return $filename;
        }

        $parts        = explode('.', $filename);
        $ext        = array_pop($parts);
        $filename    = array_shift($parts);

        foreach ($parts as $part)
        {
            if ( ! in_array(strtolower($part), $this->allowed_types) OR $this->mimes_types(strtolower($part)) === FALSE)
            {
                $filename .= '.'.$part.'_'; // Line 994.
            }
            else
            {
                $filename .= '.'.$part;
            }
        }

        $filename .= '.'.$ext;

        return $filename;
    }