according to the blog https://tessel.io/blog/94736742342/getting-started-with-ble-tessel
"Making changes to the GATT profile on the module requires creating a modified version of the firmware and uploading it to the module. A guide for doing this is coming"
Has a guide been created yet and will the USB BLE device adhere to the same guide?
An informal guide has been written here.
The USB BLE device will not adhere to the same guide.
One more note: the USB dongles will use the noble and bleno libraries for master and slave mode, respectively.