Well, the device pool for your phone(s) should have a "region" assigned to it. The region will allow you to choose which codec is being used for those phones. You wouldn't be "disabling" the codec, likely you will changing it to something else. Not sure if this answers your question.
yes in service parameters under Clusterwide Parameters (Service) u will find (Strip G.729 Annex B (Silence Suppression) from Capabilities) parameter This parameter determines whether the system will advertise or negotiate Annex B for G.729 codecs. Valid values specify True or False. If the parameter is set to True, the system will not advertise or negotiate Annex B for G.729 codecs, unless that is the only matching codec (G.729b or G.729ab).
note that this parameter must be set to the same value on every node in the clustr.
1: Choose Service > Service Parameters on the Cisco CallManager.
2: Choose the server, and then choose Cisco Call Manager.
3: Under Clusterwide Parameters (Device-General), set Strip G.729 Annex B (Silence Suppression) from Capabilities to False or true.
it should be ok now :)