This function sets the default queue priority group by id.
jetapi backup -F setDefaultQueuePriority -D '_id=5d64857951d14773a519ec02' -O json
https://hostname.example.com:2087/cpsess##########/cgi/addons/jetbackup/api.cgi?function=setDefaultQueuePriority&_id=5b60448dd5ac5e4a877ac382