The Powercab and USB interface are providing a physical connection and system level connection for your operating system / PC only.
The software you run after that is up to you. 99% of our customers use the USB interface with the Powercab to allow programming of decoders via JMRI.
Example: Based on JMRI and the type of decoder you can make some changes to decoders but only what they decoder and software allows you to do. In JMRI you can choose from existing options but not create new ones. The answer to your question is based on the decoder manufacturer, the software you are using, and the limitations / requirements they have.
The behavior of the function buttons / sound buttons on a cab are not defined by the DCC system. The decoder in the locomotive defines which sounds are controlled by which button. The DCC system only sends button commands to the locomotive. How the loco responds to the button being pressed is decided by the locomotive DCC decoder. To find out what button does what function, or triggers a certain sound on your locomotive, read the documentation that came with the loco, consult the company's website or contact them by phone.