Not sure what the format would be but you could write a 'oneshot' systemd unit that depends upon bluetooth.
Originally Posted by TheCycoONE
Change after to be bluetooth.target if there is one, otherwise maybe set it to be after bluetooth.service? Keep the type to be one shot, ExecStart would be whatever the command is to pair the devices via command line. Keep the install section. RemainAfterExit i dont know if it would be yes or no for this.
Description=Set %i interface in promiscuous mode
ExecStart=/usr/bin/ip link set dev %i promisc on