How to make a custom ISO image

From Alpine Linux

ISO remastering

There are third party scripts to re-build completely custom images, like alpine-make-vm-image (works to only make a disk based VM image) and there is Alpine's original mkimg. (creates a diskless ISO file - usually what you want for QEMU and Proxmox)

An alternative

It's also possible to commit and load ISO image customizations to and from a writable partition when booting in Diskless Mode.

See also