How to custom FedoraCoreOS

Hello everyone, I am using FedoreCoreOS with OpenStack Magnum to deploy the Kubernetes clusters, I want to run some shell scripts (to download some packages, files, etc.). These shell scripts take time to complete, so I do not want to use Ignition to run these shell scripts, so is there any way that I can customize my Fedora CoreOs by running these shell scripts and repacking them into a new qcow2 image? I tried to use diskimage-builder to do it, but it did not work. Thank you for being so helpful

Ignition will not run shell scripts directly. It will install files and systemd units to the system and those will be run on first boot. You can increase the timeouts for the units to let them run longer.