Change what PulseAudio calls a device?

To improve upon dirkt's answer, due to the way shell arguments are interpreted, spaces in PulseAudio properties such as the description require double quoting:

pacmd 'update-sink-proplist device.description="My Card" '

To run a command automatically on every login, you can append it to your PulseAudio startup script (usually ~/.config/pulse/ or ~/.pulse/, without pacmd and the extra quotes.

If you don't know the name of the device you're looking for, this is the quickest way to see lists of output sinks and input sources:

pacmd list-sinks | grep name:
pacmd list-sources | grep name:

You can update the device.description with update-sink-proplist and update-source-proplist, e.g.

pacmd update-sink-proplist device.description=MyCard

I haven't figured out how to make that parse spaces in the name properly.