[sr-dev] Change SIP message within module

Hi, I am trying to develop module for Kamailio and I am wondering how to change some of SDP fields. I have function where I cast `sip_msg`'s `body` to `sdp_info` structure and within this function I am changing some fields in `sessions` and `streams` list. I am able to see changes when I am printing them after message leaves the function but Kamailio sends the original message not the changed one. Do I need somehow let the Kamailio know that the message was changed and it should rebuild `buf` field? Or I need to change directly `buf` field within `sip_msg`? If you need some more details to be able to help me with my problem please ask freely. Or maybe if I need to rephrase my problem just let me know. Thanks in advance