Howto create a tuned FreeBSD ISO on Linux

If you tweaked your i.e. your kernel.txz or base.txt don’t forget to correct your MANIFEST file (sha256sum + number of files in txz)
To compress your new txz jump inside your directory containing your file tree and do i.e.

cd /MYEXTRACTEDKERNELTXZ/
tar cfJ kernel.txz ./*

Burning

Get the exact label of the original, check /dev/disk/by-label or use a tool. Here: 12_2_RELEASE_AMD_DVD.

mkisofs -allow-leading-dots -V 12_2_RELEASE_AMD_DVD -D -R -b boot/cdboot -no-emul-boot -o FreeBSD-12.2-RELEASE-amd64-dvd1.iso DIRHOLDINGMYFILES/