Will create data type if not found, else update. Because image paths use the dataType value, it cannot be changed when using the API, data type label can be updated though.
curl -i --header "username:USERNAME" --header "password:PASSWORD" -X POST -d '{"dataTypeLabel":"Test Data Type","dataType":"TEST"}' https://volcview.wr.usgs.gov/vv-api/dataTypeApi/dataType