The isohybrid utility from syslinux has an --id option to make the MBR ID reproducible.

However, this is insufficient when combined with --uefi, as the GUIDs in the GPT partition table are always random.

I have posted a patch to the syslinux mailing list to fix this, but the project looks rather unmaintained in recent years, so I'm hoping that we may be able to get this fixed in RHEL even if it doesn't happen upstream - it looks like RHEL has patched syslinux a few times since the last upstream activity.

Please see https://www.syslinux.org/archives/2025-June/026930.html for the patch.