For beacons, it does have to be a fixed list of UUIDs. The beacons also cannot detect the device which is monitoring it. However, you could use the BTLE GATT p

For beacons, it does have to be a fixed list of UUIDs. The beacons also cannot detect the device which is monitoring it. However, you could use the BTLE GATT profile. This lets you expose services & characteristics/attributes. It does allow for two way comms.