I have looked at How do I use OverlayFS? but it doesn't answer my question.
I need to install some third party applications and they require /opt to be writable but the device I am running on has /opt on a readable rootfs. Essentially, I have a directory /opt on a read-only filesystem (lower) and let's say I have a read-write directory /mnt/optw (writable). I would like to merge /opt & /mnt/optw and mount it to /opt.
Is this possible at all?