You must be able to change this.
In the time before Scansoft bought Nuance, and then went forward under the Nuance banner, CVP (even ISN) supported connections to each company's MRCP server. The RTSP setting on the gateway had to be adjusted appropriately.
So Cisco would have been aware that different speech vendors would want the ability to have different expressions here.
Is there no config to change this? That seems bizarre. It's a standard protocol (admittedly, Cisco helped write the standard).
Regards,
Geoff