Hi,
this (or similar) topic has been discussed many times in the past.
You can create a new header or, equivalently, read and write from the packet payload.
About how to create and use a new header, refer to one of the countless header source files. The easiest one is the SeqTsHeader in src/applications/model.
About how to read/write from the payload, see the UdpEchoClient application.
Note that you can NOT use doubles in headers, and even in payloads it's quite a bad idea.
T.