Modification of a Call-ID in outgoing in-dialog requests

Hello,

Has somebody ever faced a need to change the Call-ID in outgoing in-dialog requests?

User creates the conference, it calls the conference server with INVITE and adds the participants with the REFER methods as it is described in RFC4353. Then user subscribes to the notification service and sends SUBSCRIBE method within established session (tags and call-ID are the same as in INVITE and REFER). Conference server's vendor wants this SUBSCRIBE to be sent out of dialog, i.e with call-id different than in INVITE. There is no recommendation on this in the RFC, and in my opinion this claim is not correct, BUT anyway, I wanna test this case