Few years ago, I needed a quick way to create Qemu VM's locally for testing some weird software configurations. So I made a script to pull Ubuntu cloud images and clone them into qcow2 disks, then create and register libvirt virtual machines. Part of the "magic" was creating a cloud-config ISO image that would be mounted to pre-seed the VM on first launch. It also pushed my ssh key into the VM so I wouldn't need to use passwords. Janky, but worked well for what I needed.

https://github.com/noahbailey/kvmgr/blob/master/kvmgr.sh