This is not something that we support in DEY. There are several packages that rely on a writable rootfs to work properly.
There is standard support in Yocto for this, see:
However, making this work still means that each package will need to support a read-only filesystem. Some of them support this, others would need manual patching.
Our recipes for those packages use certain logic to change things in configuration files at runtime, so they require rw access to the rootfs.
This allows us, for example, to write a unique Wi-Fi AP name for each device, using its MAC address.
You can dig into the recipes of these packages and customize them for your needs, avoiding any post installation action that meta-digi does.