[Users] Contact header modification

Hello. Is there a way to modify the contact header? For example: REGISTER REGISTER UA -----------------------------------------------> openser ----------------------------------------------------> Registrar IP:1.0.0.1 contact: ua(a)1.0.0.1 IP:1.0.0.2 contact: ua(a)1.0.0.2 The idea is to ensure that incoming call (INVITE) will path through the openser. Another setup is two interfaces, one public and one internal. Is it possible with openser? REGISTER REGISTER UA -----------------------------------------------> openser ----------------------------------------------------> Registrar IP:1.0.0.1 contact: ua(a)1.0.0.1 IP:1.0.0.2 IP:10.2.1.25 contact: ua(a)10.2.1.25 Thanks. Regards, Michel.