How to add new headers to INVITE packet with APIs?

e.g. my packet is this:

   INVITE sip:1000@192.168.2.73 SIP/2.0
   Via: SIP/2.0/UDP 192.168.2.77:5080;rport;branch=z9hG4bKUFpyDr890F1pB
   Max-Forwards: 70
   From: "Outbound Call" <sip:TCAPI_User@192.168.2.73>;tag=UZ6gtcDZvQy8e
   To: <sip:1000@192.168.2.73>
   ....
i want to add new attribute to these headers named 'Token', something like this:

   INVITE sip:1000@192.168.2.73 SIP/2.0
   Via: SIP/2.0/UDP 192.168.2.77:5080;rport;branch=z9hG4bKUFpyDr890F1pB
   Max-Forwards: 70
   From: "Outbound Call" <sip:TCAPI_User@192.168.2.73>;tag=UZ6gtcDZvQy8e
   To: <sip:1000@192.168.2.73>
   Token: gasd^@@SGHT W454v$ERYWEVGR%^#V$CSDGASF
   ....
   ....

How can i do this?!