Specifically my use case is that I am using ostree to deploy specific folders of the filesystem to some systems I manage. Because overwriting the original directories of the system is risky in case of error, I check out the directories I want inside a separate directory and then bind them during boot through /etc/fstab.
The problem arises with /etc. I want it to be part of the deployment and read-only for the most part but it would be useful to be able to make temporary modifications to it. Is there a mount option or even a different mechanism that would allow me to mount the directory I want to /etc and be able to modify it for the session but leave the original untouched?
As stated before, I do not want to remove the original directory so
cping over it is not an acceptable solution. I also need a mechanism that acts as early as the rest of the folders are mounted on boot and that is robust to errors, ie declarative mechanisms with already implemented error-handling like fstab are preferred over bash scripts.