It is currently possible to create a custom BLE service with 128-bit UUID (by using the “base_uuid” attribute of the ble.Service class), but one cannot create a custom Characteristic (using a 128-bit UUID when constructing a ble.Characteristic member). What is more, I think if one creates a custom Service with 128-bit and adds a Characteristic with a 16-bit UUID (only option at the moment), then trying to set the Characteristic’s value produces a crash. Only 16-bit UUID service with 16-bit UUID characteristic is possible.
I’ll pass this suggestion to the dev team.
This will be tested and we’ll be fixing it in the coming updates if bugged.