New Device Type Codes are registered with FieldComm Group at no charge ($0.00).
The string name (model name) associated with the Device Type Code can be updated at no charge ($0.00) while the device is not registered.
A HART-Registered device string name can be updated, however a fee will apply at the time of the request. See How do I change the model name of my HART product?
Also see How do I obtain a manufacturer ID and device type for my HART product?