Sure it is. In the enterprise parameters of your callmanager, you have one option called " URL Directories" - that's the URL to your directory and it can be changed. If you do, make sure you have the IP Phone Services SDK and read through it first... it lists the requirement for a replacement service (it can't be just any service but it needs to match certain properties of the original directory service).

If those requirements are too constraining, then the only other solution you have is to set this value to an empty string, and add the directory to the list of services.