You may add your desired headers in indexer HTTP request. You should not use "If-Modified-Since", "Accept-Charset" headers, these headers are composed by indexer itself.
"User-Agent: mnoGoSearch/version" is sent too, but you may override it.
Command has global effect for all configuration file.
HTTPHeader "User-Agent: My_Own_Agent" HTTPHeader "Accept-Language: ru, en" HTTPHeader "From: [email protected]"