Usually .mount units do not allow to replace the mount with new options, or have a duplicate mount.
Systemd brain already has -.mount unit, generated from /proc/self/mountinfo thus one cannot have a second -.mount unit with new/different options.
Thus e.g. instead of re-writing /etc/fstab like shown, it's probably best to have a .service file that executes mount to mount the overlay on top.
Alternatively all the mounts should be executed in the initramfs and not rely on systemd to mount these things.
Usually .mount units do not allow to replace the mount with new options, or have a duplicate mount. mountinfo thus one cannot have a second -.mount unit with new/different options.
Systemd brain already has -.mount unit, generated from /proc/self/
Thus e.g. instead of re-writing /etc/fstab like shown, it's probably best to have a .service file that executes mount to mount the overlay on top.
Alternatively all the mounts should be executed in the initramfs and not rely on systemd to mount these things.