If you do actually already have a /opt directory and have a squashfs filesystem the only thing you can do to make it writable is to overmount it. Since you have room available on the /usr/local/etc I recommend that you overmount there which is an EXT3 filesystem to avoid problems. To do this issue the following commands:
Originally Posted by eruisi
That's it your /opt will now be writable. You can put that mount command "mount -o bind /usr/local/etc/opt /opt" at the end of /usr/local/etc/rcS so that the overmount occurs automatically on boot up. Also if the /opt does exist and is not empty you will need to copy it to /usr/local/etc/opt before you issue the overmount (mount -o bind) command.
# mkdir /usr/local/etc/opt
# mount -o bind /usr/local/etc/opt /opt
This previous command will do that for you.
cp -r /opt /usr/local/etc
If a /opt directory do not already exist then you are out of luck; you will need to unpack your firmware; add the /opt ; repack firmware and flash your media player.