[Users] SDP Invite message modification.

I need to proxy and modify the Invite SDP. Can I do this from the cfg or do I need to look at a module like nathelper to modify the SDP? Below is an example Inbound to openser ---Non-Working SDP--- v=0 o=nt01-1w-lax 1234 1146761158 IN IP4 152.92.17.27 s=sip call t=0 0 m=audio 38936 RTP/AVP 0 18 101 c=IN IP4 152.92.17.27 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15 converted to - > Outbound to my gateway v=0 o=ast12345sg 1220177409 1220177409 IN IP4 152.92.17.27 s=- c=IN IP4 152.92.17.27 t=0 0 a=sendrecv m=audio 18006 RTP/AVP 0 18 18 a=fmtp:18 annexb=no a=fmtp:18 annexb=yes TIA, Shane