Yes. I solved it not by using questfish, but with virt-customize.
Modified the image with
virt-customize -a ~/debian-12-genericcloud-amd64-20240507-1740.qcow2 \
--run-command "printf 'Package: *\nPin: release n=trixie\nPin-Priority: 50' >> /etc/apt/preferences" \
--run-command "printf...