[Users] Changing 'expires' value in response to REGISTER

And the beat goes on... I 've got a bunch of Snom's that have a minimum register interval of 1 minute. I *know* that I can get them to register every 30 seconds if I set the 'expires' value in the Contact header of the '200 OK' response to the REGISTER request appropriately (whew) e.g., instead of returning Contact: <sip:jake.foobaz@1.2.3.4:49154>;expires=60 I return Contact: <sip:jake.foobaz@1.2.3.4:49154>;expires=30 The question is - how do I change the 'expires' value? append_to_reply() isn't relevant - i don't want another header subst() on the request's 'Expires' header isn't useful since build_contact() seems to extract it's values from the original request. Any changes I made to it seem to be ignored Any ideas? cheers