Setting up the autoinstall is done by writing a user-data.yaml cloud-init file, then booting the kernel with
autoinstall ds=nocloud-net\;s=http://autoinstall-server/
But iterating on this user-data.yaml file is quite cumbersome.
It should be possible to restart this install process without rebooting and changing the kernel command line (Just restarting install process does not work, it is stuck a “Preparing Ubuntu”). This should of course also be possible after a successful install when blocking reboot via late-commands: ....