Is it possible to modify the destination UDP port number for outgoing SIP request/response?

I am working on a sec-agree extension implementation for Kamailio and after negotiating the IPSec tunnel parameters I need to redirect the messages to the new port number. I checked the code and looks like the destination port is determined mainly by the VIA headers, which doesn't work for me. Is it possible to achieve this without messing up with the core?

Best regards,

Tsvetomir